MORPHOLOGICAL  STUDIES.  ON  THE  HEAD 
AND  MOUTH -PARTS  OF  THE 
THYSANOPTERA 


BY 


AivVAH  Peterson. 


TKfc  LIBRARY  •* 

Wk\'  OF  THE 
liSWBSiTY  OF  SLUISiS 


REPRINTED-  EROM 

ANNALS  OF  THE  ENTOMOLOGICAL/  SOCIETY  OF  AMERICA 
Volume  VIII— No.  i 


Columbus,  Ohio 
March,  1915 


THE  'LIBRARY 
OF  THE 

UHWEBS5TY  Of  BJJMB 


MORPHOLOGICAL  STUDIES  ON  THE  HEAD 
AND  MOUTH -PARTS  OF  THE 
THYSANOPTERA 


BY 


Alvah  Peterson. 


* 


MORPHOLOGICAL  STUDIES   ON   THE   HEAD  AND 
MOUTH-PARTS  OF  THE  THYSANOPTERA.* 

By  Alvah  Peterson. 

TABLE  OF  CONTENTS. 


PAGE 

I.    Introduction   20 

II.    Methods  ,   23 

III.  Acknowledgments   24 

IV.  Fixed  Parts  of  the  Head   24 

Head-capsule   24 

Clypeus  and  Labrum   27 

Compound  Eyes   28 

Ocelli   29 

Tentorium  or  Internal  Head-Skeleton   29 

V.    Movable  parts  of  the  Head   34 

Antennae   35 

Labium   35 

Maxillae  .   36 

Mandibles   43 

VI.    Pharynx   48 

VII.    Salivary  Glands   51 

VIII.    Head-glands   54 

IX.    Summary   55 

X.    Bibliography   57 


INTRODUCTION. 

The  small  insects  of  the  order  Thysanoptera  have  four 
long,  narrow,  membranous,  flat,  fringed  wings.  Only  a  few 
veins  are  present  in  the  wings  and  when  at  rest  they  are  laid 
horizontally  along  the  back.  The  sucking  mouth-parts  form  a 
cone  at  the  caudo-ventral  margin  of  the  head-capsule.  The 
maxillae,  in  part,  and  the  left  mandible  are  modified  into 
piercing  organs  and  enclosed  within  the  mouth-cone.  The 
mandibles,  clypeus  and  maxillary  sclerites  are  asymmetrical. 
The  tarsi  are  two-jointed,  "bladder-like  at  the  distal  end  and 
without  claws.    The  metamorphosis  is  incomplete. 

The  order  is  divided  into  two  suborders,  Terebrantia  and 
Tubulifera.  The  more  important  distinguishing  characters 
of  these  are  as  follows:  The  female  of  the  Terebrantia  has  a 
.saw-like  ovipositor.  This  is  wanting  in  the  female  of  the 
Tubulifera.  In  the  Terebrantia  the  terminal  segment  of  the 
abdomen  of  the  female  is  conical,  while  that  of  the  male  is 
rounded.  In  the  Tubulifera  the  distal  segment  of  the  abdomen 
is  tubular  in  both  sexes.    One  or  more  longitudinal  veins 


*  Contribution  from  the  Entomological  Laboratories  of  the  University  of 
Illinois,  No.  42. 


20 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  21 

extend  from  the  proximal  to  the  distal  end  of  the  wings  in  the 
Terebrantia,  while  only  one,  partially  developed,  median 
vein  occurs  in  the  Tubulifera. 

The  Terebrantia  are  divided  into  two  families,  Aeolothripidae 
and  Thripidae,  while  only  one  family,  Phloeothripidae,  occurs  in 
the  Tubulifera.  It  is  generally  stated  by  investigators  in  this 
field  that  the  Terebrantia  are  the  more  generalized  and  of  the 
two  families  in  this  suborder  the  Aeolothripidae  are  the  more 
primitive.  The  following  brief  summary  of  the  evidence  as 
discussed  by  Uzel  in  his  "Monographic  der  Ordnung  Thy- 
sanoptera," page  22,  supports  the  above  statement. 

The  wing  characters  of  the  Terebrantia  are  more  generalized 
than  those  of  the  Tubulifera.  The  wings  of  the  Terebrantia 
possess  one  or  more  complete  longitudinal  veins  and  in  some 
cases  cross  veins,  while  the  Tubulifera  have  only  one  partially 
developed  longitudinal  vein  and  no  cross  veins.  Cross  veins 
among  the  Terebrantia  are  present  only  in  the  family  Aeo- 
lothripidae. The  antennae  of  most  Aeolothripidae  are  nine- 
segmented  while  in  all  other  thrips  except  the  genus  Heter- 
othrips  there  are  six  to  eight  segments  found.  The  maxillary 
palpi  of  the  Aeolothripidae  are  four-segmented,  while  those  of 
the  Thripidae  are  usually  three-segmented  and  those  of  the 
Phloeothripidae  are  composed  of  two  long  segments.  The 
labial  palpi  of  the  Aeolothripidae  are  always  four-segmented 
while  those  of  other  thrips  have  but  two  segments.  The 
above  data  permit  the  assumption  that  the  Terebrantia  are 
more  primitive  than  the  Tubulifera.  This  assumption  is 
substantiated  by  the  comparative  studies  of  the  suborders 
made  in  this  paper. 

The  primary  purpose  of  this  research  is  to  reach  as  definite 
a  conclusion  as  possible  in  respect  to  the  interpretation  of  the 
asymmetrical  mouth-parts  of  the  Thysanoptera.  The  litera- 
ture of  this  subject  shows  a  decided  diversity  of  views  as  to 
their  homology  and  function.  Some  investigators  consider 
the  mouth-parts  as  fitted  for  biting,  and  others  as  fitted  for 
sucking.  The  more  recent  workers,  while  agreeing  that  they 
are  of  a  sucking  type,  yet  disagree  as  to  the  homology  of  the 
mouth-parts.  Besides  the  study  of  the  mouth-parts,  many 
interesting  head  structures  have  been  observed.  Of  these  the 
pharynx,  salivary  glands  and  head-glands  are  discussed  and 
figured. 


22  Annals  Entomological  Society  of  America    [Vol.  VIII, 


In  view  of  the  limited  nature  of  the  morphological  studies 
of  former  workers,  specimens  of  as  many  species  of  thrips  as 
possible  were  secured  for  this  work  in  order  that  an  extensive 
view  of  the  conditions  in  the  order  might  be  observed.  Twelve 
or  more  species  were  used  and  of  these  the  following  nine  were 
identified:  (1)  Heliothrips  femoralis  Reuter,  (2)  Frankliniella 
tritici  Fitch,  (3)  Thrips  physapus  Linne,  (4)  Cephalothrips 
yuccae  Hinds,  (5)  Haplothrips  verbasci  Osborn,  (6)  Thrips 
tabaci  Lindeman,  (7)  Chirothrips  manicatus  Haliday,  (8) 
Anaphothrips  striatus  Osborn,  (9)  Limothrips  cerealium 
Haliday. 

The  first  five  species  in  the  above  list  are  very  abundant  in 
the  vicinity  of  Urbana  and  as  living  material  was  necessary 
for  certain  methods  of  preparation  used,  the  most  of  my  obser- 
vations were  made  on  these.  Fortunately  these  have  proven 
to  be  typical  and  also  comparatively  easy  to  dissect  and  section. 
Heliothrips  femoralis  was  present  thruout  the  year  in  its 
nymphal  and  adult  stages  in  the  city  and  university  green- 
houses. Cephalothrips  yuccae  was  found  thruout  the  year 
between  the  closely  appressed  leaves  of  the  crown  of  the  yucca 
plant,  Yucca  filamentosa.  Its  nymphal  stages  are  abundant 
from  April  to  December.  Only  the  adult  stages  of  the  following 
were  found:  Frankliniella  tritici  occurs  in  great  numbers 
in  the  flowers  of  peonies,  roses,  composites,  etc.  Thrips 
physapus  was  very  abundant  in  the  flowers  of  dandelions  and 
Haplothrips  verbasci  can  be  secured  the  year  around  on  mullein. 
Of  the  above  five  genera,  Heliothrips,  Frankliniella  and  Thrips 
belong  to  the  suborder  Terebrantia  while  Cephalothrips  and 
Haplothrips  belong  to  the  suborder  Tubulifera.  The  nymphs 
of  Heliothrips  and  Cephalothrips  and  the  adults  of  all  five 
species  mentioned  have  received  similar  treatment  and 
observation. 

Thruout  the  following  discussions  the  structures  as  they 
exist  in  the  generalized  Terebrantia  are  considered  first  and 
the  Tubulifera  are  compared  with  them.  The  generic  names 
have  been  used  in  the  different  discussions  and  on  the  figures 
since  only  a  single  species  of  each  genus  has  been  considered. 
The  term  nymph  is  used  in  the  following  pages  to  designate 
the  feeding,  active,  immature  stages.  In  most  cases  only  the 
older  nymphs  were  used,  however,  a  few  observations  were 
made  on  the  early  instars,  but  these  did  not  differ  from  the 


uiuc 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  23 

later  instars.  The  term  semi-pupa  is  used  in  this  paper  for 
the  semi-quiescent  instar  just  before  the  adult  stage  and  it  is 
only  referred  to  in  the  suborder  Tubulifera. 

METHODS. 

For  general  purposes  thrips  should  be  killed  in  boiling  water 
and  preserved  in  70  per  cent,  alcohol.  When  only  the  chitinized 
parts  are  desired,  living  or  preserved  specimens  should  be  boiled 
for  ten  or  fifteen  minutes  in  a  10  per  cent,  solution  of  potassium 
hydroxide,  then  reboiled  in  water  to  remove  the  alkali,  and 
finally  preserved  in  70  per  cent,  alcohol.  Living  material 
treated  in  the  above  manner  is  better  than  preserved  material, 
for  preservation  in  alcohol  tends  to  make  the  specimens  too 
brittle  for  careful  dissection. 

The  use  of  a  Leitz  binocular  microscope  made  possible  the 
dissection  of  the  minute  mouth-parts.  A  number  of  media 
were  tried  in  which  to  make  dissections;  carbol-aniline  oil 
proved  to  be  the  best.  Its  good  qualities  are  that  it  evaporates 
slowly  and  will  clear  specimens  from  any  grade  of  alcohol 
above  50  per  cent.  If  it  be  desirable  to  stain  with  safranin 
or  orange  G  the  stain  can  be  dissolved  in  95  per  cent,  alcohol 
and  will  readily  mix  with  the  carbol-aniline  oil. 

The  staining  of  the  material  for  dissection  with  safranin 
proved  to  be  very  useful  in  differentiating  the  almost  colorless 
mouth-parts  of  some  of  the  species.  In  using  aniline  oil  in  any 
form  one  precaution  must  be  observed ;  as  much  as  possible  of  the 
oil  should  be  removed  with  a  blotting  paper  or  a  dry  rag  or  by 
replacing  the  carbol-aniline  oil  with  carbol-xylene  or  xylene 
before  mounting  in  balsam.  If  the  oil  be  not  removed  the 
media  in  which  the  parts  are  immersed  will  eventually  darken. 

Material  for  sections  was  fixed  with  hot  (80°  C.)  corrosive 
sublimate  (saturated  corrosive  sublimate  in  35%  alcohol 
plus  2%  of  glacial  acetic  acid)  for  15  to  30  minutes,  which  was 
replaced  by  70%  alcohol  containing  a  few  drops  of  iodine 
for  24  or  more  hours. 

Paraffin  having  a  melting  point  of  52-54  C.  gave  a  suf- 
ficiently firm  medium  in  which  to  cut  sections  as  thin  as  five 
microns.  Erhlich's  and  Delafield's  haematoxylins  were  used 
for  staining  sections  on  slides  and  orange  G.  or  safranin  for 
counter-staining.  The  best  results  were  obtained  by  staining 
punctured  specimens  in  toto  for  24  hours  in  Delafield's 
haematoxylin  or  from  3  to  7  days  in  borax  carmine. 


24  Annals  Entomological  Society  of  America    [Vol.  VIII, 


ACKNOWLEDGMENTS. 

This  investigation  was  carried  on  under  the  supervision  of 
Dr.  A.  D.  MacGillivray  and  Dr.  J.  W.  Folsom,  and  to  these 
men  I  am  greatly  indebted  for  the  sincere  interest  shown  and 
the  many  valuable  suggestions  received.  For  the  use  of  the  data 
on  the  tentorial  structures  and  their  relations  in  insects  in 
general  referred  to  in  this  paper,  I  wish  to  express  my  thanks 
to  Dr.  A.  D.  MacGillivray,  who  allowed  me  the  free  use  of  his 
unpublished  manuscript ;  and  to  Miss  Margaret  Washington  for 
the  loan  of  drawings  of  the  tentorium.  I  am  indebted  to  Mr. 
J.  D.  Hood,  of  the  U.  S.  Biological  Survey,  for  the  identification 
of  the  following  five  species:  Heliothrips  femoralis  Reuter, 
Frankliniella  tritici  Fitch,  Thrips  physapus  Linn.,  Cepha- 
lothrips  yuccae  Hinds,  and  Haplothrips  verbasci  Osborn;  to 
Dr.  A.  F.  Shull,  of  the  University  of  Michigan,  who  kindly 
furnished  several  species  of  named  thrips ;  Euthrips  ( =  Franklin- 
iella) tritici  Fitch,  Thrips  tabaci  Lindeman,  Chirothrips  man- 
icatus  Haliday  and  Anaphothrips  striatus  Osborn;  to  Professor 
H.  Garman,  who  supplied  me  with  a  few  specimens  of  Limoth- 
rips  cerealium,  the  species  he  used  in  making  his  observations; 
to  Dr.  W.  E.  Hinds  for  identifications  and  information,  and 
to  Professor  S.  A.  Forbes  and  Dr.  J.  S.  Kingsley  for  corrections 
and  suggestions. 

FIXED  PARTS  OF  THE  HEAD. 

In  the  order  Thysanoptera  the  gross  arrangement  of  the 
head  and  mouth-parts  (fig.  1,  2r  5,  8,  and  11.)  is  homologous 
with  the  corresponding  arrangement  of  the  head  and  mouth- 
parts  of  a  generalized  homopteron.  The  cone-like  mouth- 
parts  are  attached  to  the  caudo-ventral  portion  of  the  head- 
capsule  and  project  caudad  between  the  prothoracic  legs,  and 
the  antennae  are  located  at  the  extreme  cephalic  margin  of 
the  head  between  the  compound  eyes  (fig.  1  and  8). 

Head-capsule  (fig.  1,  2,  5,  7,  8,  9,  and  11). — Head  structures 
in  thrips  differ  in  many  respects  from  those  of  a  generalized 
insect.  In  the  head-capsule  nearly  all  of  the  sclerites  are  com- 
pletely united  and  all  traces  of  sutures  have  been  lost.  On 
account  of  this  union  the  following  areas  of  the  head,  front 
(fr.),  vertex  (vt.),  genae  (g.),  and  occiput  (o.),  are  designated 
only  in  a  general  way  on  the  figures.    The  labrum  and  the 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  25 

asymmetrical  clypeus  are  the  mesal  pieces  on  the  ventral 
aspect  of  the  mouth-cone.  The  compound  eyes  are  located 
at  the  latero-cephalic  corners  of  the  head-capsule,  and  the 
ocelli  when  present  are  between  the  compound  eyes  on  the 
dorsal  aspect  of  the  head. 

Heliothrips  femoralis  (fig.  1,  2,  5,  7,  12,  13,  and  19). — A  line 
extending  between  the  vertex  and  the  mouth-cone  on  the  head 
of  a  nymph  of  Heliothrips  has  a  dorso- ventral  position,  while  a 
similar  line  on  the  head  of  an  adult  has  a  cephalo-caudal 
direction.  The  position  of  this  line  or  axis  in  the  nymph 
suggests  a  similarity  to  the  position  of  the  head  of  an  orthopteron 
(Acrididae) ,  while  the  position  of  the  head  of  the  adult  is  similar 
to  the  position  of  the  head  of  an  homopteron  (Cicada). 

The  head-capsule  of  the  nymph  is  non-reticulated  and 
slightly  chitinized,  while  that  of  the  adult  is  highly  reticulated 
and  heavily  chitinized.  The  mouth-cone  of  the  nymph  occupies 
more  than  one-half  of  the  cephalic  aspect  of  the  head-capsule 
and  extends  ventro-cephalad,  while  in  the  adult  it  is  com- 
paratively smaller  and  projects  ventro-caudad. 

Two  similar  caudal  projections  (c.  a.)  arise  from  the  ventro- 
caudal  margin  of  the  head-capsule  of  the  nymph  and  extend 
for  a  short  distance  as  narrow  pieces  between  the  maxillary 
sclerites  (mx.  s.)  and  the  submentum  (sm.).  In  the  adult 
of  Heliothrips  the  caudal  projections  (c.  a.)  differ  from  those 
of  the  nymph  in  that  they  are  decidedly  asymmetrical.  The 
left  projection  is  broadly  joined  to  the  head-capsule  while  the 
broad  right  projection  has  a  narrow,  neck-like  attachment. 
This  striking  asymmetry  is  possibly  due  to  the  excessive 
lateral  extension  of  the  clypeus  toward  the  right  side.  The 
asymmetry  of  the  caudal  projections  of  other  adult  Terebrantia 
such  as  Thrips  physapus  Linne  (fig.  3  and  6)  is  not  as  prominent 
as  that  found  in  Heliothrips.  The  caudal  projections  articulate 
along  their  dorsal  sides  against  certain  sclerites  of  the  prothorax. 

The  asymmetry  of  the  head-capsule  of  the  nymph  and  adult 
is  very  evident  in  a  frontal  view  (fig.  1  and  13).  About  half-way 
between  the  meson  and  the  left  side  of  the  head-capsule  on  the 
ventral  margin  of  the  front  there  is  a  decided  recurrent  angle 
which  is  very  distinct  in  the  adult.  The  thickenings,  depres- 
sions, and  invaginations  on  the  frontal  area  of  the  head  will  be 
discussed  under  the  internal  head-skeleton. 


26  Annals  Entomological  Society  of  America    [Vol.  VIII, 


Cephalothrips  yuccce  (fig.  8,  9,  11,  17,  18,  and  20). — A  line 
extending  between  the  vertex  and  the  mouth-cone  on  the  head 
of  a  nymph  or  adult  of  Cephalothrips  has  a  cephalo-caudal 
position  and  thus  in  all  its  stages  the  position  of  the  head- 
capsule  resembles  the  position  of  the  head  of  an  homopteron 
(Cicada.).  The  nymph  of  Cephalothrips  is  very  different  from 
the  nymph  of  Heliothrips. 

The  head-capsule  of  the  nymph  and  adult  is  smooth  and 
non-reticulated.  The  mouth-cone  of  the  nymph  occupies 
about  one-half  the  ventral  aspect  of  the  head  (fig.  17),  while  in 
the  adult  it  is  reduced  to  about  one-third  the  ventral  aspect 
of  the  head  (fig.  8).  This  reduction  is  clearly  shown  in  the 
semi-pupal  stage  (fig.  20).  The  dotted  line  across  the  head 
indicates  approximately  the  point  of  attachment  of  the  mouth- 
cone  as  it  would  be  in  an  active  nymph.  This  line  is  dis- 
tinguishable in  the  early  stages  of  the  semi-pupa  by  a  difference 
in  the  staining  quality  of  the  two  areas  on  the  ventral  aspect 
of  the  head.  With  the  reduction  of  the  mouth-cone  of  the 
Tubulifera,  striking  modifications  have  resulted  in  the  form 
of  the  clypeus,  the  left  maxillary  sclerite,  and  the  piercing 
organs.  The  modification  and  the  reduction  of  these  parts 
during  metamorphosis  are  of  great  value  in  determining  their 
homology. 

Symmetrical,  caudal  projections  (c.  a.)  are  present  at  the 
ventro-lateral  margins  of  the  head-capsule  of  the  nymph  and 
adult.  The  caudal  projections  of  the  adult  are  prominent  and 
terminate  in  distinct  acetabula  which  fit  against  certain  sclerites 
of  the  prothorax  (p.  s.).  This  arrangement  permits  of  a  dorso- 
ventral  movement  of  the  head. 

The  asymmetry  of  the  caudal  margin  of  the  front  of  the 
adult  is  not  prominent  and  in  the  nymph  no  asymmetry  can 
be  seen.  The  recurrent  angle  in  the  adult  is  located  in  a 
position  similar  to  that  in  Heliothrips. 

An  unidentified  suture  (s.)  occurs  on  the  lateral  aspect 
of  the  head-capsule  of  the  adult  dorsad  of  the  caudal  projec- 
tions. There  is  also  an  indication  of  a  suture  along  the  dorso- 
caudal  margin  of  the  head.  This  suture  along  with  the 
thickenings  and  invaginations  on  the  frontal  and  genal  areas 
of  the  head  will  be  considered  later  with  the  discussion  of  the 
internal  head-skeleton. 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  27 

Clypeus  and  Labrum. — The  clypeus  and  labrum  are  the 
mesal  pieces  on  the  ventral  aspect  of  the  mouth-cone. 

Heliothrips  femoralis  (fig.  1  and  13). — The  adult  and  nymph 
show  no  marked  differences  in  the  form  of  the  clypeus  and 
labrum.  The  clypeus  (cl.)  is  the  large  asymmetrical  piece, 
and  the  convex  piece  at  its  distal  end  is  the  labrum  (Ir.) .  Garman 
and  other  workers  have  considered  the  area  cephalad  of  the 
line  f  as  the  clypeus  and  the  area  ventrad  of  this  line  as  the 
labrum.  With  this  interpretation  one  meets  with  considerable 
difficulty  in  homologizing  the  parts  in  the  two  suborders. 
If  the  line  f  is  a  suture,  it  can  not  be  the  clypeo-labral  suture, 
but  must  be  the  proximal  margin  of  the  clypeus.  The  area 
between  this  so-called  suture  and  the  front  is  a  broad  hyaline 
membrane  (me.).  In  safranin-stained  material,  it  is  slightly 
colored  while  in  sagittal  sections  stained  in  haematoxylin  it 
shows  a  decided  blue  tinge.  The  above  interpretation  of  the 
line  f  may  be  correct,  but  a  better  interpretation  seems  to  be 
that  it  marks  the  point  where  the  heavily  chitinized,  proximal 
end  of  the  clypeus  becomes  more  or  less  membranous,  and  thus 
permits  the  dorsal  and  lateral  movements  of  the  mouth-cone. 
The  line  f  is  located  in  a  deep  fold  from  which  point  the  mouth- 
cone  extends  in  a  caudo-ventral  direction  in  the  adult  and 
cephalo- ventrad  in  the  nymph.  A  distinct  line  or  suture 
(s.)  can  be  seen  extending  from  the  recurrent  angle  on  the  front 
to  the  left  lateral  end  of-  the  line  f.  This  suture  is  the  left 
lateral  margin  of  the  clypeus  and  shows  distinctly  in  the  nymph 
of  Heliothrips  (fig.  13)  and  in  the  adult  of  Thrips  physapus 
(fig.  3).  This  evidence  supports  the  interpretation  that  the' 
entire  area  from  the  front  to  the  small  convex  labrum  is  the 
clypeus.  Garman's  drawing  of  Limothrips  cerealium  shows 
clearly  the  above  clypeal  and  labral  areas  even  tho  he  interprets 
the  parts  differently. 

The  clypeus  (cl.)  is  an  asymmetrical  triangle  with  its  right 
latero-cephalic  angle  decidedly  more  cephalad  than  its  left 
latero-cephalic  angle.  The  left  margin  of  the  clypeus  is  a 
comparatively  straight  line  from  the  front  to  the  labrum  and 
nearly  parallel  with  the  meson,  while  the  right  margin  in  the 
adult  is  a  curved  line  and  extends  at  a  decided  angle  to  the 
meson  from  the  labrum  to  the  point  of  attachment  of  the  right 
caudal  projection  with  the  head-capsule.  This  unique  asym- 
metry is  characteristic  of  all  the  Terebrantia  examined. 


28  Annals  Entomological  Society  of  America    [Vol.  VIII, 

Cephalothrips  yuccce  (fig.  8  and  17). — In  the  nymph  of 
Cephalothrips  the  clypeus  (cl.)  is  a  long,  V-shaped,  nearly 
symmetrical  piece  attached  to  the  caudal  margin  of  the  front 
(fr.).  The  fronto-clypeal  suture  between  the  clypeus  and  the 
head-capsule  is  wanting.  The  small,  distinct,  convex  piece 
at  the  distal  end  of  the  clypeus  is  the  labrum  (lr.).  The  clypeus 
of  the  semi-pupal  stage  is  smaller  than  that  of  the  nymph 
on  account  of  the  reduction  of  the  mouth-cone.  It  is  sym- 
metrical and  shows  a  distinct  fronto-clypeal  suture,  but  the 
clypeo-labral  suture  is  not  present,  however,  it  is  indicated  by 
indentations  on  the  lateral  margins  of  the  clypeus  near  the 
distal  end  of  the  mouth-cone.  The  ventral  margin  of  the 
labrum  is  bilobed  indicating  its  future  adult  structure.  Within 
the  semi-pupal  parts  the  developing  adult  structures  can 
be  seen. 

In  the  adult  (fig.  8)  the  clypeus  and  labrum  have  been 
modified  thru  the  reduction  of  the  mouth-cone,  but  they  are 
distinctly  differentiated  by  sutures  and  color  differences. 
The  above  interpretation  of  the  clypeus  and  labrum,  which  is 
the  one  given  by  Muir  and  Kershaw,  agrees  with  the  nymph 
and  adult  condition  found  in  all  Tubulifera  observed  and  it 
also  explains  the  condition  found  in  the  Terebrantia.  Garman's 
interpretation  of  the  clypeus  and  labrum  in  the  Terebrantia 
presents  difficulties  when  an  attempt  is  made  to  apply  it  to 
the  conditions  found  in  the  Tubulifera. 

Compound  Eyes. — The  compound  eyes  of  Heliothrips  (fig. 
12,  13  and  19)  are  present  in  the  nymph  as  small,  oval  areas 
on  the  lateral  aspects  of  the  head-capsule  in  the  dorso-caudal 
region.  There  are  five,  round,  indistinct  bodies  in  each  elevated 
area.  In  the  nymph  of  Cephalothrips  (fig.  17  and  18)  two 
similar,  elevated,  small,  oval  areas  are  present  on  the  cephalo- 
lateral  aspects  of  the  head,  but  these  possess  no  facets  or  round 
bodies.  In  the  adult  stage  of  both  species  (fig.  1,  2,  5,  7,  8,  9, 
and  11)  there  is  a  large,  reniform  area  filled  with  facets,  cover- 
ing the  latero-cephalic  areas  of  the  head.  In  the  adult  of 
Heliothrips  the  eyes  protrude  beyond  the  general  curvature  of 
the  head,  the  facets  are  scattered,  few  in  number  and  variable 
in  size.  From  a  ventral  view  six  large,  opaque  facets  can  be 
seen.  These  larger  facets  retain  their  muddy  brown  color, 
and  do  not  become  clear  and  transparent  as  do  the  remainder 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  29 

of  the  facets  when  they  have  been  treated  with  potassium 
hydroxide.  In  the  adult  of  Cephalothrips  the  eyes  do  not 
protrude  from  the  head-capsule,  the  facets  are  numerous, 
clear,  and  all  approximately  of  the  same  size. 

Ocelli. — The  ocelli  as  far  as  observed  are  three  in  number. 
They  are  situated  on  the  dorsal  aspect  of  the  head  between  the 
compound  eyes  in  the  form  of  a  triangle  with  the  median  ocellus 
on  the  cephalic  side.  In  the  two  species  figured  the  ocelli  of 
Heliothrips  (fig.  7)  are  clear  oval  bodies  located  on  a  small, 
elevated,  triangular  area,  while  the  ocelli  of  Cephalothrips 
(fig.  9)  are  clear,  circular  bodies,  larger  than  the  facets  of  the 
compound  eyes,  more  distant  from  each  other  than  those  of 
Heliothrips  and  not  elevated  above  the  general  plane  of  the 
head-capsule.    No  traces  of  ocelli  were  found  in  the  nymphs. 

Tentorium  or  Internal  Head-skeleton. — Under  this 
heading  only  those  internal  structures  found  in  the  head  that 
pertain  to  the  tentorium  will  be  considered.  For  other  internal 
parts  the  discussions  on  the  maxillae,  pharynx  and  salivary 
glands  should  be  consulted. 

One  finds  within  the  head  of  a  generalized  insect  a  definite 
arrangement  of  rod-  and  plate-like  structures  which  go  to 
support  the  internal  organs  and  furnish  points  of  attachment 
for  muscles.  These  rods  or  plates  extend  from  three  pairs 
of  openings  on  the  head-capsule.  These  openings  are  known 
as  the  invaginations  of  the  anterior  arms,  dorsal  arms  and 
posterior  arms  of  the  tentorium.  The  invaginations  of  the 
anterior  arms  are  usually  associated  with  the  lateral  margins 
of  the  clypeus  and  with  one  of  the  points  of  articulation  of  the 
mandibles.  The  invaginations  of  the  dorsal  arms  are  associated 
with  the  points  of  attachment  of  the  antennae.  The  invagi- 
nations of  the  posterior  arms  are  associated  with  the  occipital 
foramen,  and  the  point  of  attachment  of  the  maxillae.  These 
generalized  relations  become  modified  in  the  various  orders 
and  families  of  insects.  The  invaginations  may  disappear  and  the 
rods  and  plates  undergo  striking  changes  or  become  atrophied. 
The  important  point,  however,  is  that  in  all  orders  of  insects, 
so  far  as  observed,  the  invaginations  and  the  arms  of  the  tent- 
orium are  always  associated  with  the  appendages  named. 
These  associations  exist  in  thrips  and  an  attempt  will  be  made 
to  show  that  they  have  an  important  bearing  on  the  homology 
of  their  mouth-parts. 


30  Annals  Entomological  Society  of  America    [Vol.  VIII, 

On  account  of  the  close  relation  existing  between  the 
Homoptera  and  the  Thysanoptera,  a  comparison  will  be  made 
between  the  internal  head-structures  of  Cicada  and  those  of 
thrips.  Figure  29  is  a  lateral  view  of  the  entire  tentorium 
of  Cicada  showing  the  invaginations  and  the  arms.  The 
invaginations  of  the  anterior  arms  of  the  tentorium  (i.  a.) 
occur  at  the  ventro-lateral  ends  of  the  clypeus  while  the  dorsal 
arms  are  invaginated  (i.  d.)  just  ventrad  of  the  antennae. 
Between  these  two  pairs  of  invaginations  distinct,  thin,  broad, 
chitinized  plates  extend  which  are  the  anterior  arms  of  the 
tentorium  (a.  a.).  The  invaginations  of  the  posterior  arms 
(i.  p.)  are  found  on  the  lateral  margins  of  the  occipital  foramen 
adjacent  to  the  maxillary  plates  described  by  Muir  and  Ker- 
shaw. These  invaginations  give  rise  to  the  broad,  plate-like 
posterior  arms  (p.  a.)  which  nearly  surround  the  occipital 
foramen.  A  small  chitinized  rod  extends  across  the  occipital 
foramen  between  the  dorsal  ends  of  the  posterior  arms.  This 
rod  is  the  body  of  the  tentorium  (b.  t.)  and  from  its  mesal 
portion  two  long,  slender  rods  arise  which  extend  cephalad 
(d.  a.)  and  unite  with  the  invaginations  of  the  dorsal  arms 
(i.  d.).  These  two  rods  are  the  dors'al  arms  of  the  tentorium. 
In  Cicada  the  ventral  ends  of  the  posterior  and  anterior  arms 
unite  on  each  side  (xc.)  and  between  these  united  arms  there 
extends  across  the  meson  a  distinct  plate  or  bridge  (zc).  The 
usual  association  between  the  appendages  of  the  head  and  the 
tentorium  among  insects  may  be  found  in  Cicada;  that  is,  the 
invaginations  of  the  posterior  arms  (i.  p.)  are  near  the  point 
of  attachment  of  the  maxillary,  piercing  organs  with  the  head- 
capsule;  the  mandibles  are  associated  with  the  anterior  arms 
but  on  account  of  their  great  length  and  the  excessive  develop- 
ment of  the  clypeus,  they  are  not  connected  near  the  invagina- 
tions of  the  anterior  arms  (i.  e.)  but  connect  with  the  head- 
capsule  slightly  laterad  of  the  anterior  arms  near  the  invagina- 
tions of  the  dorsal  arms ;  and  the  invaginations  of  the  dorsal 
arms  (i.  d.)  are  adjacent  to  the  antennae. 

As  mentioned  before,  the  internal  head-skeleton  of  thrips 
undergoes  considerable  modification  and  this  is  well  illustrated 
in  the  various  heads  figured.  In  the  nymph  of  Heliothrips 
(fig  12,  13,  19  and  28)  the  tentorial  structures  are  nearly  all 
present,  while  in  the  adult  of  Cephalothrips  (fig.  8  and  33) 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  31 


extensive  atrophy  has  taken  place  and  those  tentorial  parts 
which  still  remain  can  only  be  interpreted  by  comparison 
with  the  more  generalized  conditions  in  the  nymphs. 

On  the  cephalic  aspect  of  the  head  of  a  nymph  of  Heliothrips 
(fig.  13)  two  sets  of  invaginations  can  be  seen.  One  pair 
exists  on  the  ventral  margin  of  the  front  (i.  a.)  and  the  second 
pair  (i.  d.)  a  short  distance  dorsad  of  these.  Since  the  invagina- 
tions on  the  ventral  margin  of  the  front  are  close  to  the  lateral 
edges  of  the  wide  clypeus,  they  actually  occur  on  the  lateral 
aspects  of  the  head-capsule.  This  is  especially  true  of  the 
invaginations  on  the  right  side.  Distinct  chitinous  arms  extend 
between  the  invaginations  on  each  side  (a.  a.).  The  invagi- 
nations, as  described,  are  homologous  with  the  two  pairs  of 
invaginations  on  the  cephalic  aspect  of  the  head  of  Cicada. 
The  two  invaginations  on  the  ventral  margin  of  the  front 
are  believed  to  be  the  invaginations  of  the  anterior  arms  of 
the  tentorium  (i.  a.)  while  the  invaginations  dorsad  of  these 
are  the  invaginations  of  the  dorsal  arms  of  the  tentorium 
(i.  d.).  The  rods  between  the  invaginations  on  each  side  are 
the  anterior  arms  (a.  a.).  Chitinized  thickenings  (d.  a.) 
extend  dorso-caudad  from  each  of  the  invaginations  of  the 
dorsal  arms  (i.  d.)  and  these  thickenings  on  reaching  the  caudal 
margin  of  the  head-capsule  turn  caudad  and  run  parallel 
with  the  caudal  margin  of  the  head  (p.  a.)  to  the  distal  ends 
of  the  caudal  projections  (c.  a.).  On  comparison  with  Cicada 
the  dorso-caudal  extensions  that  project  from  the  invaginations 
of  the  dorsal  arms  to  the  caudal  margin  of  the  head  are  homol- 
ogous with  the  dorsal  arms  of  the  tentorium  (d.  a.)  while  the 
chitinized  thickenings  along  the  lateral  margins  of  the  occipital 
forearm  (p.  a.)  are  considered  as  homologous  with  the  posterior 
arms  of  the  tentorium.  In  thrips  the  body  of  the  tentorium 
is  wanting,  consequently  the  dorsal  arms  (d.  a.)  connect  directly 
with  the  posterior  arms  (p.  a.).  The  invaginations  for  the 
posterior  arms  (i.  p.)  were  not  identified  in  any  of  the  thrips 
examined.  In  a  few  cases  it  seemed  as  though  the  invaginations 
were  present  near  the  ventral  end  of  the  posterior  arms  (p.  a.) 
where  the  thickenings  (x.)  on  the  ventral  margin  of  the  head- 
capsule  came  in  contact  with  the  posterior  arms.  Thus  far 
the  tentorium  of  a  nymph  of  the  Terebrantia  can  be  homologized 
with  the  tentorium  of  Cicada. 


32  Annals  Entomological  Society  of  America    [Vol.  VIII, 


The  differences  which  occur  between  the  tentorium  of  a 
Cicada  and  a  thrips  can  be  largely  accounted  for  in  the  dif- 
ferences between  the  head-structures.  The  head-capsule  of  a 
thrips  is  elongated  cephalo-caudad  while  this  extension  of  the 
head-capsule  of  a  Cicada  is  short.  Furthermore  in  a  Cicada 
the  clypeus  is  large  and  occupies  the  greater  part  of  the  cephalic 
aspect  of  the  head  but  this  is  not  so  in  thrips.  The  invaginations 
of  the  dorsal  arms  (i.  d.)  in  thrips  are  apparently  not  associated 
with  the  antennae.  This  seemingly  lost  association  is  undoubt- 
edly due  to  the  excessive  cephalic  or  dorsal  growth  of  the  head- 
capsule.  The  location  of  the  invaginations  of  the  anterior 
arms  of  the  tentorium  (i.  a.)  in  thrips  resembles  the  location 
in  a  generalized  insect  since  they  are  near  the  cephalo-lateral 
corners  of  the  clypeus  and  not  near  the  distal  ends  of  the 
clypeus  as  in  Cicada. 

The  following  tentorial  structures  are  present  in  thrips 
which  are  difficult  to  account  for  on  the  basis  of  the  homology 
with  the  structures  in  Cicada.  A  distinct  thickening  extends 
along  the  caudal  or  ventral  margin  of  the  head-capsule  between 
the  caudal  projections  (x.  and  z.).  This  thickening  is  present 
in  all  thrips.  In  the  nymph  of  Heliothrips  the  portion  of  the 
thickening  (x.)  between  the  ventral  end  of  the  right  anterior 
arm  (a.  a.)  and  the  right  posterior  arm  (p.  a.)  is  wanting.  The 
above  thickening  may  be  secondary  or  possibly  may  be  homol- 
ogized  with  the  union  of  the  ventral  ends  of  the  anterior  and 
posterior  arms  of  Cicada  (xc.  and  zc).  In  all  the  thrips 
examined,  distinct,  chitinous,  ental  projections  arise  from  the 
invaginations  of  the  dorsal  arms.  These  projections  are  not 
present  in  Cicada. 

In  considering  the  tentorium  of  thrips  figured  in  this  paper, 
a  distinct  atrophy  of  certain  portions  and  parts  can  be  seen.  In 
the  adult  of  Heliothrips  (fig.  1  and  27)  a  thickening  occurs 
(x.  and  z.)  along  the  caudo-ventral  margin  of  the  head-capsule 
and  from  this  thickening  other  thickenings  (p.  a.)  arise  which 
extend  to  the  caudal  projections  (c.  a.)  of  the  head-capsule. 
Of  the  anterior  arms  (a.  a.)  only  the  left  one  is  present.  The 
left  anterior  arm  is  located  in  a  depressed  line  extending  between 
the  invagination  of  the  left  dorsal  arm  and  the  recurrent 
angle  on  the  caudal  margin  of  the  front.  The  dorsal  arms 
(d.  a.)  are  wanting  and  also  the  posterior  arms  (p.  a.)  except 
for  a  small  portion  on  the  caudal  projections  (c.  a.)  of  the 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  33 


head-capsule.  The  invaginations  of  the  anterior  arms  are  very- 
indistinct  in  this  species  due  to  the  thick,  highly  chitinized 
and  reticulated  nature  of  the  head-capsule.  This  characteristic 
also  makes  it  difficult  to  differentiate  the  tentorial  thickenings. 
However  in  Thrips  physapus  (fig.  3  and  6)  the  invaginations 
of  the  anterior  (i.  a.)  as  well  as  the  tentorial  thickenings  are 
readily  made  out  in  dissected  heads  that  have  been  stained. 
The  invaginations  of  the  dorsal  arms  (i.  d.)  with  their  ental 
projections  show  very  clearly  in  the  adult  of  Heliothrips  and 
likewise  in  all  thrips. 

In  the  nymph  of  Cephalothrips  (fig.  22)  a  still  greater 
reduction  of  the  tentorium  apparently  exists.  This  apparent 
loss,  however,  may  be  due  to  the  fact  that  it  is  impossible  to 
distinguish  all  the  parts  on  account  of  the  extremely  thin  and 
membranous  nature  of  the  head-capsule.  Only  the  invagin- 
ations of  the  dorsal  arms  (i.  d.)  with  their  ental  projections 
show  very  clearly.  By  careful  staining  one  can  distinguish 
a  thickening  (a.  a.)  occupying  the  position  of  the  left  anterior 
arm  of  the  tentorium.  This  thickening  extends  from  the 
invagination  of  the  left  dorsal  arm  (i.  d.)  to  the  point  where  the 
asymmetrical  piercing  organ  (1.  md.)  unites  with  the  head- 
capsule.  In  this  feature  there  is  a  remarkable  similarity 
between  the  nymphal  head  of  the  Tubulifera  and  the  adult 
head  of  the  generalized  Terebrantia. 

The  tentorium  of  the  adult  of  Cephalothrips  resembles 
somewhat  that  of  Heliothrips.  In  Cephalothrips  the  anterior 
arms  of  the  tentorium  are  atrophied  but  the  invaginations 
of  the  dorsal  arms  with  their  projections  are  very  distinct 
and  the  invaginations  of  the  anterior  arms  can  be  identified 
in  dissected  material  that  has  been  stained,  if  a  careful  examina- 
tion is  made  of  the  caudal  boundary  of  the  head-capsule  (z.) 
at  the  point  where  the  lateral  margins  of  the  clypeus  are  in 
contact  with  the  front.  Besides  the  thickenings  that  are  similar 
to  those  of  Heliothrips  two  thickenings  extend  cephalad  (mx.  p.) 
on  the  lateral  areas  of  the  head-capsule.  These  cephalic- 
extending  thickenings  clearly  arise  from  the  thickenings  (z.) 
about  the  caudo-ventral  margin  of  the  head-capsule  and 
terminate  in  enlarged,  elevated  ends  which  possess  acetabula 
in  which  the  proximal  pieces  of  the  paired,  piercing  organs 
(mx.)  articulate.  One  can  readily  see  that  these  mandibular 
pillars,  as  Muir  and  Kershaw  call  them,  are  of  a  tentorial  origin. 


34  Annals  Entomological  Society  oj  America    [Vol.  VIII, 

A  distinct  strip  (st.)  is  present  on  the  caudal  margin  of  the 
head-capsule  of  Cephalothrips  and  extends  between  the  short 
sutures  (s.)  which  arise  from  the  latero-caudal  margin.  Stained 
material  shows  clearly  that  this  area  (st.)  is  structurally  dif- 
ferent from  the  head-capsule  cephalad  of  it.  On  the  ends 
of  this  area  (st.)  two  depressions  are  present  which  are  similar 
in  many  respects  to  the  invaginations  of  the  tentorium.  If 
these  are  invaginations  of  the  posterior  arms  then  this  is  a 
thickening  composed  of  the  union  of  the  posterior  arms  about 
the  dorsal  margin  of  the  occipital  foramen.  This  interpretation 
is  rather  questionable  since  no  invaginations  of  the  posterior 
arms  have  been  seen  in  the  more  generalized  thrips. 

As  a  conclusion  to  the  above  discussion  on  the  internal 
head-skeleton,  the  following  statements  are  of  importance. 
The  tentorium  and  the  associated  mouth-parts  of  an  homopteron 
such  as  Cicada  can  be  interpreted  on  comparison  with  the  same 
parts  in  a  generalized  insect.  The  arms  of  the  tentorium  and 
their  respective  invaginations  in  the  nymph  of  one  of  the 
Terebrantia  can  be  homologized  with  the  tentorial  parts  of  a 
Cicada.  On  the  basis  of  this  homology  the  specialized  and 
atrophied  conditions  existing  in  the  adults  of  the  Terebrantia 
and  in  the  nymphs  and  adults  of  the  Tubulifera  can  be  inter- 
preted. 

Furthermore,  on  the  basis  of  this  homology  between  the 
tentorium  of  thrips  and  other  insects  an  attempt  will  be  made 
to  demonstrate  the  association  of  the  mandibles  and  the 
maxillae  with  their  respective  tentorial  parts.  This  should 
give  conclusive  evidence  as  to  the  correct  interpretation  of 
the  two  sets  of  piercing  organs.  See  discussion  on  mandibles 
and  maxillae  for  this  demonstration. 

MOVABLE   PARTS   OF  THE  HEAD. 

The  movable  parts  of  the  head  will  be  considered  in  the 
following  order:  antennae,  labium,  maxillae  and  mandibles. 
In  the  discussion  of  the  movable  appendages  those  of  the 
generalized  Terebrantia  will  be  considered  first  and  then  the 
homologous  structures  of  the  Tubulifera  will  be  compared 
with  them. 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  35 

Antennae  (fig.  4) . — The  antennae  of  the  adult  of  Helio- 
thrips  are  about  twice  the  length  of  the  head-capsule,  eight- 
segmented  and  reticulated  with  chitinous  elevations  cor- 
responding to  the  reticulations  (rt.)  on  the  head-capsule. 
The  shape,  size,  reticulated  character  and  the  setal  arrangement 
are  shown  in  the  figure.  Segments  one,  two,  six,  seven  and 
eight  are  of  a  brownish  color  similar  to  the  head-capsule  while 
the  remaining  segments  are  but  slightly  pigmented.  The 
distal  end  of  segment  four  gives  rise  to  a  thin,  hyaline,  two- 
branched  sense  cone  (s.  c).  The  sense  cones  are  not  present 
in  the  antennae  of  the  nymph.  Except  for  this  the  antennae 
of  the  nymph  are  structurally  similar  to  those  of  the  adult. 

The  antennae  of  the  nymph  and  adult  of  Cephalothrips 
resemble  each  other  and  are  of  the  same  number  of  segments, 
eight,  providing  the  very  small  pieces  at  the  distal  ends  of  the 
nymphal  antennae  are  considered  as  segments.  In  the  first 
stages  of  the  semi-pupa  (fig.  20)  the  antennae  appear  as 
mere  buds  at  the  cephalic  margin  of  the  head-capsule.  As  the 
insect  becomes  older,  the  antennal  cases  increase  in  size  and 
length  until  they  extend  around  the  lateral  margins  of  the  head- 
capsule.  A  late  stage  of  the  semi-pupal  instar  shows  seg- 
mentation on  the  distal  portions  of  the  antennal  cases.  The 
eight-segmented  antennae  of  the  adult  are  about  one  and  one- 
third  times  longer  than  the  dorsal  aspect  of  the  head-capsule 
and  have  a  yellow  color  thruout,  except  the  two  basal  segments, 
which  are  of  a  brown  tinge.  The  general  shape,  size  and  setal 
arrangement  of  the  segments  is  shown  in  figure  10.  Segments 
three,  four,  five  and  six  each  possess  at  their  distal  end  a  pair 
of  simple,  hyaline,  spine-like  sense  cones  (s.  a).  The  sense 
cones  are  wanting  in  the  nymph. 

Labium. — The  mouth-parts  of  Hemiptera  are  fitted  '  for 
sucking.  In  this  adaptation  the  labium  is  modified  into  a  long, 
trough-like  beak,  enclosing  the  bristle-like  mandibles  and 
maxillae.  The  mouth-parts  of  Thysanoptera  are  also  fitted 
for  sucking.  The  adaptation  in  thrips,  however,  is  not  confined 
to  the  specialization  of  one  part  of  the  mouth,  but  the  clypeus, 
labrum,  maxillary  sclerites  and  labium  together  form  a  broad 
and  blunt  mouth-cone,  enclosing  the  needle-like  mandibles 
and  maxillae.  Of  these  two  types  of  sucking  mouth-parts, 
those  of  the  Thysanoptera  more  closely  resemble  a  generalized 


36  Annals  Entomological  Society  of  America    [Vol.  VIII, 

biting  type  of  mouth.  The  arrangement  of  the  parts  of  the 
mouth-cone,  the  presence  of  maxillary  and  labial  palpi  and 
other  characteristics  in  Thysanoptera  show  this  close  similarity. 

The  labium  of  the  nymph  and  adult  of  thrips  is  similar 
(fig.  60  and  61).  The  entire  convex,  caudal  area  of  the  mouth- 
cone  is  the  labium.  From  a  caudal  view  it  is  distinctly  tri- 
angular in  outline,  with  the  apex  at  its  distal  end  and  from  a 
ventral  or  lateral  view  it  is  convex.  The  labium  is  attached 
along  its  lateral  margins  to  the  triangular,  palpus-bearing 
sclerites  (mx.  s.)  while  its  dorsal  margin  is  united  with  the  ventral 
membranous  portion  of  the  prothorax.  It  is  composed  of 
two  distinct  sclerites  separated  by  a  transverse  suture  (s.). 
The  proximal  piece  is  the  submentum  (sm.)  and  the  distal 
piece  is  the  mentum  (m.).  The  mentum  has  at  its  distal 
end  a  membranous  area  which  gives  rise  to  a  pair  of  small, 
two-segmented  palpi  (lb.  pi.).  The  distal  margin  of  the 
mentum  possesses  two  small,  chitinous  projections  considered 
by  Hinds  as  paraglossae  (pr.). 

Heliothrips  femoralis. — The  labium  of  Heliothrips  (fig.  60) 
corresponds  to  the  general  description.  The  dorso- ventral 
length  of  the  labium  is  about  the  width  of  the  submentum. 
The  ectal  surface  of  the  labium  is  slightly  reticulated. 

Cephalothrips  yuccce. — The  labium  of  Cephalothrips  (fig.  61) 
corresponds  to  the  general  description.  The  mouth-cone  of 
Cephalothrips  is  short,  consequently  the  dorso-ventral  length 
of  the  labium  is  less  than  one-half  the  width  of  its  submentum 
(s.  m.).  The  submentum  is  heavily  chitinized  along  its  proxi- 
mal margin  as  indicated  in  the  figure.  The  mesal  portion  of 
the  suture  (s.)  between  the  submentum  and  the  mentum  is 
obsolete,  but  its  lateral  ends  show  distinctly.  The  two  pro- 
jections or  paraglossae  at  the  distal  end  of  the  labium  are  united 
and  form  a  lip-like  structure  over  which  the  movable,  paired, 
piercing  organs  pass.  This  lip  is  indicated  by  shading  in 
figure  8.  - 

Maxillae. — A  pair  of  asymmetrical,  triangular,  palpus- 
bearing  sclerites  (mx.  s.)  are  situated  on  the  lateral  sides  of  the 
clypeus  and  labrum  in  the  mouth-cone  of  the  Thysanoptera 
(fig.  1  and  8).  The  palpi  (mx.  pi.)  of  these  pieces  are  usually 
two-  or  three-segmented.  A  comparison  of  these  palpus- 
bearing  sclerites  with  similar  sclerites  in  Cicada  shows  that 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  37 


they  are  homologous  with  the  so-called  maxillary  plates 
described  by  Muir  and  Kershaw.  The  segmented  palpi 
however  are  wanting  on  the  maxillary  plates  of  the  Hemiptera. 
Their  presence  in  Thysanoptera  indicates  a  more  primitive 
condition  and  also  is  conclusive  evidence  that  these  sclerites 
are  maxillary  in  origin. 

The  lateral  margins  of  the  maxillary  sclerites  (mx.  s.)  are 
turned  into  the  mouth-cone,  thus  giving  rise  to  ento-mesal 
extensions  (et.)  or  plates.  These  extensions,  toward  the  distal 
end  of  the  mouth-cone,  unite  with  the  lateral  edges  of  the 
pharynx  and  form  sheaths  or  troughs  over  which  the  needle- 
like portions  of  the  paired  piercing  organs  (mx.)  pass.  This 
is  clearly  shown  in  cross-sections  of  the  pharynx  (fig.  38-44  and 
51-57). 

Two  sets  of  piercing  organs  are  found  in  the  mouth-cone  of 
all  Thysanoptera  (fig.  22,  27,  28  and  33).  The  paired,  sym- 
metrical set  will  be  considered  first  because  of  their  relation 
to  the  maxillary  sclerites.  Each  one  of  the  paired  piercing 
organs  is  composed  of  three  parts  (mx.).  Its  distal  portion 
is  long,  grooved,  needle-like,  and  swollen  at  the  proximal  end. 
The  middle  portion  is  short  and  thick  and  separated  from  the 
distal  portion  by  a  distinct  suture  while  its  proximal  end  is 
connected  to  the  proximal  portion  by  a  movable  joint.  The 
proximal  portion  is  a  heavy  piece  and  in  some  cases  three  or 
four  times  as  long  as  the  middle  portion.  Also  its  proximal 
end  articulates  against  the  cephalic  edge  of  the  maxillary 
sclerite  (mx.  s.)  or  in  an  acetabulum  on  an  elevated  pillar 
(mx.  p.)  arising  from  the  head-capsule.  This  articulation  in 
all  cases  is  either  directly  or  indirectly  associated  "with  the 
maxillary  sclerite.  The  presence  of  two  movable  joints  in 
this  piercing  organ  makes  its  extension  into  a  straight  line  pos- 
sible. This  extension  occurs  when  the  organ  functions.  When 
the  paired  piercing  organs  are  extended  beyond  the  mouth-cone 
the  grooved,  needle-like  piercing  portions  interlock  and  such  a 
union  naturally  makes  an  effective  tool.  This  interlocking  is 
readily  seen  in  sectioned  material  (fig.  25). 

The  muscles  which  bring  about  the  extension  of  the  paired 
piercing  organs  (mx.)  are  attached  to  the  proximal  pieces. 
Each  extensor  muscle  is  connected  with  the  ental  surface  of  the 
maxillary  sclerite  and  the  mesal  edge  of  the  proximal  piece 
when  the  piercing  organs  (mx.)  are  within  the  head-capsule. 


38 


Annals  Entomological  Society  of  America    [Vol.  VIII, 


The  above  characteristics  concerning  the  maxillary  sclerites 
(mx.  s.)  and  the  paired  piercing  organs  (mx.)  may  be  found  in 
all  thrips  as  far  as  observed  and  one  can  safely  infer  that  the 
similar  parts  in  all  thrips  are  homologous  and  should  have  the 
same  interpretation  thruout  the  order.  In  a  like  manner  it 
will  be  found  that  a  similar  homology  exists  between  the 
asymmetrical  piercing  organs  of  all  thrips.  This  homology 
eliminates  the  suggestion  offered  by  Muir  and  Kershaw  that 
in  the  two  suborders  of  the  Thysanoptera  a  distinct  difference 
of  interpretation  of  the  piercing  organs  might  be  possible. 

Heliothrips  femoralis  (fig.  1,  2,  5,  12,  13,  19,  27,  and  28).— 
The  maxillae  of  Heliothrips  are  in  general  typical  of  the  sub- 
order Terebrantia  and  accord  with  the  general  description 
of  the  maxillae  just  given.  The  maxillary  sclerites  (mx.  s.) 
of  the  nymph  and  adult  resemble  each  other  except  that  the 
palpi  of  the  nymph  are  four-segmented  while  those  of  the 
adult  consist  of  only  two  long  segments.  The  palpi  of  some  of 
the  more  generalized  adult  Aeolothripidae  are  four-segmented 
and  thus  the  four-segmented  palpi  of  the  nymph  indicate  a 
generalized  condition.  The  maxillary  sclerites  (mx.  s.)  are 
decidedly  asymmetrical.  This  asymmetry  is  more  pronounced 
in  the  adult  (fig.  1).  The  proximal  ends  of  the  maxillary  sclerites 
of  the  adult  are  not  in  direct  contact  with  the  head-capsule. 
There  are  distinct  membranous  areas  (me.)  between  them. 
In  this  particular  species  the  membranous  areas  (me.)  continue 
from  the  cephalic  margin  of  the  maxillary  sclerites  to  the  bases 
of  the  palpi  where  the  membranes  broaden  and  surround  the 
proximal  segments.  The  membranous  strip  on  the  left  maxil- 
lary sclerite  is  more  extensive  than  the  one  on  the  right.  The 
ento-mesal  extensions  (et.)  arising  from  the  lateral  margins 
of  thejmaxillary  sclerites  resemble  closely  the  general  descrip- 
tion of  these  parts  and  they  can  be  readily  made  out  in  figures 
28  and  39  to  44. 

The  paired  piercing  organs  of  Heliothrips  (fig.  27  and  28, 
mx.)  are  but  slightly  longer  than  the  maxillary  sclerites  and 
this  is  true  of  the  Terebrantia  in  general.  The  structure  of 
their  paired  piercing  organs  resembles  the  general  description 
of  these  parts.  The  proximal  piece  in  the  nymph  is  L-shaped 
and  the  base  of  the  L  articulates  along  the  dorsal  margin  of  the 
maxillary  sclerite  (mx.  s.).    The  proximal  piece  in  the  adult, 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  39 

likewise  articulates  against  the  cephalic  margin  of  the  maxillary 
sclerite  and  has  an  L-shape,  but  the  base  of  the  L  is  greatly 
reduced  and  the  erect  portion  is  longer,  heavier  and  of  the 
same  thickness  thruout.  The  above  relation  between  the 
paired  piercing  organs  and  the  maxillary  sclerites  is  true  of  all 
Terebrantia  as  far  as  observed  (fig.  14,  21  and  32).  Since 
the '  paired  piercing  organs  in  the  Terebrantia  are  directly 
connected  with  the  cephalic  margin  or  the  latero-cephalic 
corners  of  the  maxillary  sclerite,  one  may  conclude,  as  Garman 
has  already  done  in  his  work  on  Limothrips  cerealium,  that  these 
piercing  organs  are  parts  of  the  maxillae.  If  such  is  the  case 
the  paired  piercing  organs  may  be  modified  lacinia  as  Garman 
has  suggested.  According  to  Garman  and  other  workers 
these  organs  consist  of  only  two  pieces,  but  in  all  species  observed 
three  distinct  pieces  can  be  found.  The  suture  between  the 
needle-like  distal  portion  and  the  middle  piece  is  wanting  in 
the  figures  of  other  workers. 

Karl  Jordan  and  other  workers  have  interpreted  the  paired 
piercing  organs  (mx.)  as  mandibles.  Jordan  worked  with 
Heliothrips  haemorrhoidalis,  a  form  closely  related  to  Helio- 
thrips  femoralis.  His  proof  is  largely  founded  on  the  state- 
ment that  the  embryonic  development  shows  that  these  pieces 
are  mandibles.  The  evidence  in  support  of  this  statement 
is  wanting  in  both  figures  and  discussion.  He  has  but  one 
figure  of  the  embryonic  condition  and  in  this  the  relation  of  the 
so-called  mandibles  to  the  head-capsule  and  other  parts  is 
not  clear.  The  real  difficulty  with  Jordan's  interpretation 
rests  in  the  fact  that  he  has  wrongly  identified  the  asym- 
metrical piercing  organ  (1.  md.)  and  consequently  in  his 
search  for  mandibles  he  has  from  necessity  tried  to  show  that 
the  paired  piercing  organs  are  mandibles. 

The  conclusion  in  regard  to  the  paired  piercing  organs  of 
the  Terebrantia  is  that  they  are  portions  of  the  maxillae,  and 
the  following  additional  evidence  will  be  presented  to  sub- 
stantiate the  same. 

In  the  first  place,  if  these  paired  piercing  organs  are  mandi- 
bles, how  can  one  explain  their  three  piece  structure?  Mandibles 
usually  have  only  one  solid  piece,  but  maxillae  on  the  other  hand 
are  composed  of  several  sclerites  and  upon  modification  they 
might  assume  the  conditions  found  in  thrips.    As  to  the  exact 


40  Annals  Entomological  Society  of  America    [Vol.  VIII, 

homology  of  these  pieces  it  is  difficult  to  determine.  However, 
on  the  basis  of  the  maxillae  of  other  insects,  one  finds  that  the 
galea  is  usually  segmented  while  the  lacinia  is  not.  In  most 
sucking  insects  the  galea  is  present  and  the  lacinia  may  be 
wanting.  It  would  seem  that  the  paired  piercing  organs  were 
galea  rather  than  lacinia  as  Garman  has  suggested.  For 
convenience  of  description  the  paired  piercing  organs  will  be 
designated  as  the  maxillary  setae  (mx.). 

Strong  evidence  is  likewise  .found  in  the  relation  existing 
between  the  paired  piercing  organs  and  the  tentorium  of  the 
head.  The  maxillae  in  generalized  insects  are  associated  with 
the  invaginations  of  the  posterior  arms  of  the  tentorium  and 
this  relation  was  shown  to  be  true  with  Cicada.  On  the  basis 
of  the  homology  between  the  tentorium  of  Cicada  and  thrips 
it  was  shown  that  the  thickening  about  the  occipital  foramen  in 
the  nymph  of  Heliothrips  (p.  a.)  are  homologous  with  the 
posterior  arms  of  Cicada.  In  the  nymph  and  adult  of 
Heliothrips  the  paired  piercing  organs  are  closely  associ- 
ated with  the  ventral  or  caudal  ends  of  these  thickenings  or 
so-called  posterior  arms.  As  mentioned  before,  no  invagina- 
tion of  the  posterior  arms  of  the  tentorium  could  be  found  in 
this  genus  of  thrips;  however,  from  the  close  association  of 
the  paired  piercing  organs  with  the  posterior  arms  of  the 
tentorium  we  may  conclude  that  the  generalized  relation 
between  the  posterior  arms  of  the  tentorium  and  the  maxillae 
holds  for  thrips  as  well  as  for  more  primitive  insects. 

Further  evidence  is  found  in  the  fact  that  in  generalized 
insects  the  maxillae  are  always  attached  to  the  head-capsule 
caudad  of  the  mandibles.  As  was  pointed  out-  in  the  dis- 
cussion of  the  head-capsule  of  thrips,  the  mouth-cone  has  been 
carried  around  the  head  until  it  is  now  found  at  the  caudo- 
ventral  portion  of  the  head.  As  a  result  the  mouth-parts 
have  a  cephalo-caudal  extension  rather  than  the  generalized 
dorso-ventral  direction.  This  rotation  of  the  mouth-parts 
means  that  the  maxillae  should  connect  with  the  head-capsule 
dorsad  of  the  mandibles.  The  paired  piercing  organs  of  the 
Terebrantia  (mx.)  are  decidedly  dorsad  to  the  asymmetrical 
piercing  organ  (1.  md.),  and  it  will  be  shown  later  that  the 
asymmetrical  piercing  organ  is  a  mandible. 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  41 


Cephalothrips  yuccce. — The  maxillae  of  Cephalothrips  (fig. 
8,  11,  17,  18,  20,  22,  and  33)  are  typical  of  the  suborder  Tubu- 
lifera.  The  maxillary  sclerites  (mx.  s.)  of  the  nymph  (fig.  17) 
and  the  adult  (fig.  8)  are  dissimilar  in  comparative  size  and 
symmetry,  but  both  possess  a  two-segmented  palpus  (mx.  pi.). 
The  long  maxillary  sclerites  of  the  nymph  are  nearly  symmetrical 
while  those  in  the  reduced  mouth-cone  of  the  adult  are  asym- 
metrical. This  asymmetry  in  the  adult  is  characterized  by  a 
distinct  knob  (n.)  at  the  cephalic  end  of  the  mesal  margin 
of  the  maxillary  sclerite.  This  knob  fits  into  a  notch  on  the 
left  margin  of  the  clypeus  and  appears  to  be  a  portion  of  the 
maxillary  sclerite,  but  a  close  examination  shows  that  it  is 
only  connected  with  the  maxillary  sclerite  by  a  narrow  strip 
at  its  latero-cephalic  corner;  and  a  distinct  fissure,  which  extends 
cephalad  and  laterad  from  the  point  where  the  clypeo-maxil- 
lary  suture  turns  mesad,  separates  it  from  the  maxillary 
sclerite.  The  asymmetrical  piercing  organ  of  the  adult  is 
associated  with  the  above  asymmetry.  On  comparison  with 
the  asymmetry  found  in  the  Terebrantia  the  asymmetry  of  the 
Tubulifera  is  of  a  decidedly  different  nature. 

The  mesal  extensions  (et.)  of  the  lateral  edges  of  the  maxil- 
lary sclerites  resemble  the  general  description  of  these  parts 
(fig.  22,  33  and  35).  However,  a  unique  modification  of  these 
extensions  is  found  in  the  development  of  two  long,  trough- 
like, cephalic  extending  arms  (mx.  g.).  These  parts  serve  to 
guide  the  long  maxillary  setae  and  have  been  designated  as 
the  maxillary  guides.  These  guides  are  only  present  in  the 
Tubulifera,  and  undoubtedly  they  have  been  developed  in  this 
suborder  on  account  of  the  necessity  of  some  kind  of  a  guiding 
structure  for  the  exceedingly  long  maxillary  setae..  The  max- 
illary guides  arise  from  the  mesal  part  of  the  sheath  (et.)  that 
extends  between  the  lateral  edges  of  the  maxillary  sclerites  at 
the  distal  end  of  the  mouth-cone,  and  project  forward  into  the 
dorsal  portion  of  the  head-cavity  to  the  region  of  the  compound 
eyes.  Cross-sections  of  the  pharynx  (fig.  53  and  54)  show 
that  in  this  forward  projection  they  unite  with  the  pharynx. 
In  the  nymph  they  are  narrow  at  their  proximal  ends  but 
broadly  rounded  and  separate  at  their  distal  ends,  while  in  the 
adult  they  are  trough-like  and  their  distal  ends  are  united  in  a 
transverse  plate.    The  long  maxillary  setae  pass  around  the 


42  Annals  Entomological  Society  of  America    [Vol.  VIII, 

cephalic  ends  of  the  maxillary  guides  and  at  first  are  dorsad  of 
the  guides.  In  their  caudo-ventral  extension  they  pass  along 
the  lateral  sides  of  the  trough-like  guides  and  laterad  of  the 
pharynx  toward  the  tip  of  the  mouth-cone  beyond  which  the 
two  distal,  grooved,  needle-like  portions  interlock  and  pro- 
ject as  a  single  piercing  organ  (fig.  25).  The  maxillary  guides 
show  no  relation  to  the  tentorial  structures  of  the  head. 

The  paired  piercing  organs  (mx.)  of  Cephalothrips,  except 
for  size,  and  point  of  attachment  in  the  adult,  resemble  the 
maxillary  setae  of  Heliothrips.  The  linear  extension  of  the 
maxillary  setae  in  Cephalothrips  is  due  largely  to  the  increased 
length  of  the  distal  and  proximal  pieces.  The  large  proximal 
piece  in  the  adult  possesses  a  distinct  knob  on  its  mesal  margin 
which  serves  as  a  point  of  attachment  for  muscles.  The 
resemblance  between  the  maxillary  setae  in  the  nymph  or  adult 
of  Heliothrips  (fig.  27  or  28)  and  the  paired  piercing  organs  in 
the  nymph  of  Cephalothrips  is  very  striking  and  important. 
The  feature  of  significance  in  the  nymph  of  Cephalothrips  is  the 
point  of  attachment  of  the  paired  piercing  organs  with  the 
cephalic  margin  of  the  maxillary  sclerites.  This  shows  clearly 
that  the  paired  piercing  organs  of  Cephalothrips  are  not  only 
homologous  in  structure  but  in  point  of  articulation  with  the 
maxillary  setae  of  the  Terebrantia.  The  paired  piercing  organs 
of  the  Tubulifera  are  therefore  maxillary  setae.  The  evidence 
used  to  prove  that  the  paired  piercing  organs  of  the  Tere- 
brantia are  maxillary  in  origin  will  likewise  hold  for  the  Tu- 
bulifera with  the  exception  of  the  evidence  based  on  the  ten- 
torium, since  some  of  the  tentorial  structures  are  wanting 
in  the  nymph  of  Cephalothrips. 

The  relation  of  the  maxillary  setae  to  the  mouth-parts  in 
the  adults  of  the  Tubulifera  (fig.  33)  is  apparently  very  different 
from  the  conditions  found  in  the  Terebrantia.  The  reduction 
of  the  mouth-cone  explains  to  a  large  extent  the  characteristic 
modifications  of  this  suborder.  In  the  reduction  of  the  mouth- 
cone  the  proximal  pieces  of  the  long  maxillary  setae  (mx.)  do 
not  retain  their  point  of  articulation  with  the  maxillary  scler- 
ites but  articulate  in  acetabula  located  in  special  elevated 
maxillary  pillars  (mx.  p.)  on  the  ental  surface  of  the  head- 
capsule  cephalad  of  the  maxillary  sclerites.  This  modification 
is  a  result  of  a  mechanical  necessity.    It  would  be  impossible 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  43 

for  the  long  maxillary  setae  to  function  if  they  retained  their 
connection  with  the  reduced  maxillary  sclerites.  However, 
their  connection  with  the  maxillary  sclerites  is  not  entirely 
lost  since  the  thickenings  from  which  the  maxillary  pillars 
(mx.  p.)  arise,  extend  to  the  tentorium  (x.  and  z.),  which  is 
adjacent  to  the  maxillary  sclerites.  These  thickenings  are 
undoubtedly  derived  from  the  tentorium,  and  since  the  maxillae 
are  associated  with  them  they  are  possibly  modifications  of 
the  posterior  arms  (p.  a.). 

Muir  and  Kershaw  in  their  work  on  a  species  of  Tubulifera 
interpret  the  paired,  piercing  organs  as  mandibles.  They 
give  two  lines  of  evidence.  In  the  first  place,  they  show  that 
the  asymmetrical  piercing  organ  (1.  md.)  is  a  part  of  the 
maxillae,  consequently  the  paired  piercing  organs  must  be  man- 
dibles. Also  they  have  proved  to  their  own  satisfaction  by 
comparison  with  Rhynchota  that  the  paired  piercing  organs 
are  mandibles.  "The  paired  setae  we  consider  as  mandibles, 
homologous  to  those  of  Rhynchota."  The  first  part  of  their 
evidence  will  be  considered  later.  In  regard  to  their  own 
statement  here  quoted  there  is  considerable  doubt.  They 
present  no  satisfactory  evidence  on  this  point,  and  as  far  as 
observed,  the  relations  existing  in  Cicada  permit  of  no  such 
interpretation,  as  has  already  been  shown.  Jordan  also  studied 
individuals  of  the  Tubulifera  and  came  to  the  same  conclusions 
as  in  his  studies  on  the  Terebrantia.  The  different  inter- 
pretations of  the  paired  piercing  organs  in  the  Thysanoptera 
of  the  authors  mentioned  above  has  been  largely  due  to  an 
incomplete  comparative  study  of  the  nymphal  and  adult  stages 
of  both  the  suborders. 

Mandibles. — A  large,  heavy,  unpaired  piercing  organ 
(1.  md.)  is  present  on  the  left  side  of  the  mouth-cone  of  all 
thrips  (fig.  2,  3,  11,  12,  18,  22,  27,  28,  and  33)  while  on  the  right 
side  no  such  organ  is  found.  Berlese  figures  the  asymmetrical 
piercing  organ  as  occurring  on  the  right  side.  Undoubtedly 
this  is  a  mistake  for  in  no  case  has  such  an  occurrence  been 
recorded  by  other  workers.  This  asymmetry  of  mouth-parts 
is  unique  among  insects.  The  asymmetrical,  piercing  organ 
connects  with  the  head-capsule  at  the  point  where  the  left 
margin  of  the  clypeus  or  the  right  margin  of  the  maxillary 
sclerite  comes  in  contact  with  the  front.    It  is  composed  of 


44  Annals  Entomological  Society  of  America    [Vol.  VIII, 


two  parts,  which  are  of  about  the  same  length.  The 
distal  half  is  a  long,  heavily  chitinized,  hollow  spine,  while  the 
proximal  half  is  broader,  hollow  and  not  as  heavily  chitinized. 
Cross  and  longitudinal  sections  show  a  distinct  lumen  extending 
thruout  its  length  (fig.  26).  At  the  very  tip  of  the  spine  it 
is  impossible  however  to  be  sure  that  an  opening  is  present. 
If  such  an  opening  is  present  then  it  may  serve  as  an  exit  for  the 
secretions  from  the  glandular  tissue  within  the  basal  half  of  the 
piercing  organ.  If  the  lumen  is  not  a  duct  for  the  secretions 
but  a  blind  tube,  then  one  can  explain  its  presence  on  the  basis 
that  it  is  the  place  formerly  occupied  by  the  hypodermal  cells 
which  formed  the  cuticle  of  the  spine. 

Cross-sections  of  the  pharynx  show  how  the  asymetrical 
piercing  organ  passes  along  the  cephalic  side  of  a  left  lateral 
extension  of  the  pharynx  (fig.  40  and  41).  This  left  lateral 
extension  is  cephalad  of  the  paired  extensions  over  which  the 
maxillary  setae  pass,  and  only  occurs  on  the  left  side.  In  the 
Tubulifera  the  left  maxillary  guide  helps  to  form  this  extension 
(%•  53). 

There  are  large  muscles  attached  to  the  proximal  end  of  the 
asymmetrical  piercing  organ.  These  muscles  connect  with 
the  dorsal  aspect  of  the  head-capsule  and  on  contraction 
pull  the  asymmetrical  piercing  organ  (1.  md.)  into  the 
mouth-cone.  The  majority  of  the  specimens  examined  showed 
the  piercing  organ  protruding  from  the  concave  side  of 
the  labrum  (lr.).  Apparently  this  is  its  normal  position  and 
it  is  evidently  used  in  making  the  first  puncture  thru  the 
outer  cells  of  the  plant  tissue.  After  this  puncture  is  made 
it  is  probably  withdrawn  into  the  mouth-cone,  and  the 
long  maxillary  setae  are  then  used  to  puncture  the  inner  and 
deeper  cell-layers.  The  withdrawal  of  the  asymmetrical 
piercing  organ '  from  the  tip  of  the  mouthrcone  also  permits 
the  plant  juices  to  pass  into  the  pharynx. 

On  the  right  side  of  the  mouth-cone  a  piece  (r.  md.)  is  found 
which  is  homologous  in  position  to  that  of  the  left,  asymmetrical 
piercing  organ  (rig.  27).  In  all  cases  this  piece  arises  adjacent 
to  the  front,  between  the  clypeus  and  the  right  maxillary 
sclerite,  and  extends  to  the  right  cephalo-lateral  margin  of  the 
pharynx  and  unites  with  the  same  (fig.  40).  This  union  is 
indicated  by  a  distinct  suture  in  cross-sections  of  the  pharynx. 


1915]        The  Head  and  Month-Parts  of  Thysanoptera  45 


The  invaginations  of  the  anterior  arms  of  the  tentorium  (i.  a.) 
in  thrips  are  always  located  on  the  caudal  margin  of  the  front 
and  adjacent  to  the  asymmetrical  piercing  organ  and  the  above- 
described  piece.  This  evidence,  undoubtedly  shows  that  this 
rudimentary  piece  on  the  right  side  is  homologous  with  the 
asymmetrical  piercing  organ  on  the  left. 

Heliothrips  femoralis  (fig.  2,  5,  12,  19,  27  and  28.).— The 
left  asymmetrical  piercing  organ  and  its  right  homologous 
rudiment  are  typical  of  the  suborder  Terebrantia  and  correspond 
to  the  general  description  given  above.  These  parts  in  the 
nymph  and  adult  closely  resemble  each  other.  In  the  nymph 
(fig.  28)  the  left,  piercing  organ  is  smaller,  straighter,  and  its 
two  halves  less  differentiated  than  in  the  adult  (fig.  27).  The 
basal  half  of  the  left,  piercing  organ  is  connected  with  the  front 
by  a  narrow,  chitinized  neck.  This  connection  is  readily  seen 
in  frontal  sections  of  the  adult  and  nymph. 

The  right,  rudimentary  piece  in  the  nymph  and  adult 
extends  as  a  distinct  piece  between  the  right  cephalo-lateral 
margin  of  the  pharynx  and  the  front.  This  piece  is  homologous 
with  the  asymmetrical  piercing  organ  (1.  md.)  and  resembles 
somewhat  its  basal  half.  The  distinguishing  differences  in  these 
two  are  their  size  and  the  union  of  the  right  piece  with  the 
pharynx.  Jordan  represents  a  prominent  projection  on  the 
right  margin  of  the  pharynx  of  Heliothrips  haemorrhoidalis. 
This  probably  represents  the  asymmetrical  piece  above  de- 
scribed. Garman  found  in  his  work  on  Limothrips  a  small, 
right,  asymmetrical  structure  which  he  considered  to  be  a 
rudimentary  piece  homologous  with  the  left,  piercing  organ. 
These  two  pieces  Garman  designated  as  mandibles.  This 
interpretation  agrees  with  my  own  observations.  Garman's 
own  words  are,  "The  organ  has  every  appearance  of  being  a 
mandible.  Its  form  and  its  relation  to  the  other  mouth- 
parts  and  to  the  epicranium  all  indicate  this.  Nothing  cor- 
responding to  this  conspicuous  organ  is  apparent  on  the  right 
side  of  the  head  unless  a  very  small,  chitinous  structure  under 
the  edge  of  the  clypeus  is  a  rudiment  of  the  organ  for  this  side." 
Garman  records  the  structure  of  the  left  mandible  as  con- 
sisting of  one  solid  piece.  The  writer  however,  considers  the 
left  mandible  as  composed  of  two  parts.  At  least  in  all  thrips 
examined  a  distinct  constriction  occurs  between  the  distal 
spine  and  the  large  proximal  portion,  and  to  all  appearances  a 


46  Annals  Entomological  Society  of  America    [Vol.  VIII r 


suture  is  located  here.  Without  any  question  the  mandible 
is  hollow,  as  heretofore  explained.  The  following  evidence  goes 
to  show  that  the  asymmetrical  piercing  organs  of  the  Tere- 
brantia  are  mandibular  in  origin. 

In  the  first  place,  as  Garman  has  already  mentioned,  the 
structure,  position,  and  point  of  connection  of  the  asym- 
metrical piercing  organ  with  the  head-capsule  are  strong 
mandibular  characteristics.  It  has  already  been  pointed  out 
that  the  invaginations  for  the  tentorial  arms  on  the  front  of 
thrips  are  homologous  with  the  invaginations  of  the  tentorial 
arms  on  the  cephalic  aspect  of  the  head  of  Cicada.  The  in- 
vaginations of  the  anterior  arms  of  the  tentorium  on  the  caudal 
margin  of  the  front  (i.  a.)  are  adjacent  to  the  point  of  connection 
of  the  left  and  right  asymmetrical  organs  (1.  md.  and  r.  md.). 
This  relation  shows  that  the  asymmetrical  piercing  organs  of 
the  Terebrantia  are  undoubtedly  mandibles  since  in  generalized 
insects  mandibles  are  usually  associated  with  the  invaginations 
of  the  anterior  arms  of  the  tentorium. 

Furthermore,  mandibles  in  generalized  insects  are  always 
connected  with  the  head-capsule  cephalad  of  the  maxillae.  In 
the  nymph  of  Heliothrips  the  asymmetrical  piercing  organs 
are  connected  cephalad  of  the  maxillary  setae  but  in  the  adult 
on  account  of  the  change  of  position  of  the  mouth-cone  these 
connections  are  ventrad  of  the  maxillary  setae.  This  relation 
in  the  Terebrantia  shows  clearly  that  the  asymmetrical  pierc- 
ing organs  are  mandibular  in  origin. 

Karl  Jordan  interprets  the  left,  asymmetrical  piercing  organ 
(1.  md.)  as  a  modified  epipharynx.  He  bases  his  conclusion 
upon  embryological  studies.  The  one  embryo  figured  shows 
the  asymmetrical  organ  as  the  upper  portion  of  the  anterior 
end  of  the  alimentary  canal.  The  base  of  the  so-called  epi- 
pharynx is  also  connected  with  the  head-capsule.  He  con- 
cludes from  this  figure  that  when  the  adult  stage  is  reached  the 
epipharynx  loses  all  connection  with  the  alimentary  canal  and 
becomes  more  firmly  attached  to  the  head-capsule.  The 
above  hypothesis  in  regard  to  the  behavior  of  the  epipharynx 
is  contrary  to  the  relations  of  these  parts  in  other  insects. 
Jordan  likewise  failed  to  account  for  the  right,  rudimentary 
piece  (r.  md.).  On  the  whole  Jordan's  interpretation  is  very 
unsatisfactory,  for  it  does  not  explain  numerous  relations  here 
pointed  out. 


1915] 


The  Head  and  Mouth-Parts  of  Thysanoptera 


47 


Cephalothrips  yuccce  (fig.  11,  18,  22,  26,  33,  34,  35  and  36).— A 
striking  similarity  exists  between  the  ental  view  of  the  mouth- 
parts  of  a  nymph  of  Cephalothrips  (fig.  22)  and  the  adult  stage 
of  Heliothrips  (fig.  27).  This  similarity  is  particularly  notice- 
able in  respect  to  the  structure  and  position  of  the  asymmetrical 
piercing  parts.  On  the  basis  of  this  similarity  it  is  possible 
to  derive  the  correcf  interpretation  of  the  asymmetrical, 
piercing  organs.  The  left  mandible  (1.  md.)  in  the  nymph  is 
a  long,  nearly  straight,  stout,  two-segmented  structure  and  con- 
nects with  the  caudal  margin  of  the  front  (f.)  at  the  point  where 
the  maxillary  sclerite  and  clypeus  unite  with  the  head-capsule. 
Between  this  point  of  connection  and  the  invagination  of  the 
left  dorsal  arm  of  the  tentorium  a  thickening  occurs  (a.  a.). 
This  thickening  is  the  anterior  arm  of  the  tentorium  and  can  be 
seen  in  carefully  stained  and  dissected  material. 

The  right,  rudimentary  mandible  in  the  nymph  of  Cephal- 
othrips is  represented  by  a  distinct  chitinized  thickening  be- 
tween the  clypeus  and  the  right  maxillary  sclerite.  The 
distal  end  of  this  thickening  (r.  md.)  unites  with  the  right 
lateral  margin  of  the  pharynx  as  seen  in  cross-sections  of  the 
adult  pharynx  (fig.  55  and  56).  Figures  33  and  35  do  not 
show  this  connection  because  of  the  spreading  of  the  heads. 

The  above  nymphal  evidence  clearly  demonstrates  the 
homology  between  the  asymmetrical  mandibular  parts  of  a 
species  of  Tubulifera  and  those  of  a  species  of  Terebrantia. 
The  evidence  used  in. proving  that  the  asymmetrical  piercing 
organs  of  the  Terebrantia  are  mandibles  is  equally  applicable 
in  demonstrating  that  the  asymmetrical  parts  in  the  Tubulifera 
are  also  mandibles.  One  exception  however  occurs  in  the  fact 
that  in  the  nymph  of  Cephalothrips  the  invaginations  for  the 
anterior  arms  have  not  been  identified  along  with  other  ten- 
torial structures. 

The  mandibular  parts  of  the  adult  (fig.  33)  undergo  a 
distinct  modification  due  to  the  reduction  in  the  size  of  the 
mouth-cone.  In  this  change  the  left  mandible  (1.  md.)  retains 
its  position  between  the  clypeus  and  the  left  maxillary  sclerite, 
but  in  so  doing  the  heavy,  proximal  portion  turns  and  forms 
a  half  circle.  This  modification  has  resulted  in  the  formation 
of  a  distinct  notch  (n.)  in  the  clypeus  and  the  left  maxillary 
sclerite.    It  has  also  resulted  in  the  uniting  of  the  meso-cephalic 


48  Annals  Entomological  Society  of  America    [Vol.  VIII, 

corner  of  the  maxillary  sclerite  and  the  base  of  the  left  man- 
dible. The  right  mandible  in  the  reduction  of  the  mouth-cone 
has  given  rise  to  a  distinct,  crook-like,  ental  projection.  The 
above  modifications  are  typical  for  the  suborder  Tubulifera  as 
far  as  observed. 

Muir  and  Kershaw  interpreted  the  left,  asymmetrical 
piercing  organ  as  a  part  of  the  maxillae  in  their  work  on  one 
species  of  Tubulifera.  "The  unpaired  setae  arises  from  the  left 
maxillae  and  is  a  part  thereof."  It  is  readily  understood  how 
such  an  error  came  about,  since  only, the  adult  stage  of  a  single 
species  of  Tubulifera  was  studied.  The  connection  of  the  left 
asymmetrical  piercing  organ  in  the  adult  with  the  left  maxil- 
lary sclerite  is  secondary.  This  connection  does  not  show  in 
the  nymph. 

PHARYNX. 

If  one  examines  the  mouth-cone  of  various  species  of  thrips,  a 
short,  heavily  chitinized,  ham-shaped  piece  is  always  found  just 
beneath  the  clypeus.  Stained  and  sectioned  material  shows 
clearly  that  this  piece  is  a  structural  modification  of  the  ali- 
mentary canal,  fitted  for  sucking  and  homologous  with  the 
pharynx  of  sucking  insects  (fig.  5,  6,  19,  27,  35,  38-46,  48,  49 
and  52-59).  Jordan  figures  this  particular  piece  and  calls  it 
the  hypopharynx  of  the  pharynx,  while  his  epipharynx  is  what 
we  have  interpreted  to  be  the  left  mandible. 

Structurally  the  pharynx  consists  of  one  piece  except  for  a 
small,  chitinized,  transverse  area  (t.  a.)  at  the  caudo-dorsal  end 
(fig.  46  and  48).  However,  in  respect  to  size  and  shape  the 
pharynx  is  divided  into  two  regions.  The  ventral  half  is  a 
small,  chitinized  tube  which  opens  within  the  ental  groove 
of  the  labrum,  while  the  dorsal  half  widens  out  into  a  broad, 
thick  region.  The  entire  pharynx  resembles  a  gourd  dipper 
which  has  had  removed  from  one  side  almost  one-half  of  its 
enlarged  portion,  and  across  this  cavity  there  has  been  placed 
a  concave,  elastic  membrane  (e.)  to  which  muscles  (d.  m.) 
are  attached.  On  the  caudal  side  of  the  enlarged  portion  there 
are  two  small  openings.  Glandular  ducts  (d.)  pass  thru  these 
openings  and  pour  their  secretions  into  the  sucking  chamber. 

When  the  pharynx  is  sectioned  in  one  of  three  planes, 
frontal,  sagittal  and  transverse,  it  shows  a  centrally  located 
canal  extending  thru  its  entire  length.    This  lumen  starts  with 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  49 


the  mouth  and  continues  dorsad  of  the  pharynx  as  the  oesopha- 
gus (oe.).  Transverse  sections  of  the  pharynx  show  that  it  is 
firmly  connected  on  its  caudo-lateral  aspects  with  the  maxillary 
guides  (mx.  g.)  and  the  mesal  extensions  (et.  and  1.  et.)  from  the 
lateral  margins  of  the  maxillary  sclerites  and  the  labium. 
Over  the  lateral  extensions  (et.)  the  maxillary  setae  (mx.)  pass. 
The  left  mandible  (1.  md.)  passes  over  an  extension  on  the 
left  lateral  margin  of  the  pharynx  cephalad  of  the  above 
extensions  and  the  right,  rudimentary  mandible  (r.  md.) 
unites  with  the  right  margin  of  the  pharynx.  The  above 
extensions  and  supports  that  connect  with  the  pharynx  serve 
to  hold  it  in  position  while  the  large  muscles  are  dilating  its 
elastic  membrane  (e.).  The  above  facts  in  regard  to  the 
pharynx  hold  for  all  thrips  as  far  as  observed. 

Heliothrips  femoralis. — Figures  38-46  and  58  give  a  much 
better  idea  of  the  general  structure  of  the  pharynx  of  Helio- 
thrips than  a  lengthy  discussion,  consequently  only  the  im- 
portant and  exceptional  facts  will  be  pointed  out.  The  trans- 
verse sections  (fig.  37-44)  begin  with  a  section  thru  the  com- 
missures between  the  supraoesophageal  and  suboesophageal 
ganglia  and  end  at  the  tip  of  the  mouth-cone.  Every  second  or 
third  section,  ten  microns  in  thickness,  has  been  figured.  In 
this  series  the  lumen  (1.),  lateral  extensions  (et.  and  1.  et.), 
piercing  organs  (mx.,  1.  md.  and  r.  md.),  elastic  membrane 
(e.),  and  muscles  •  (d.  m.)  are  shown.  The  connection  of  the 
muscles  along  the  meson  of  the  elastic  membrane  is  character- 
istic of  the  Terebrantia.  The  large  nucleated  and  cross- 
striated  muscles,  the  dilators  of  the  pharynx  (fig.  58,  d.  m.), 
extend  cephalad  into  the  cavity  of  the  head-capsule  and  unite 
with  the  ventral  and  cephalic  areas.  Two  or  more  of  these  large 
muscle  bands  unite  with  a  more  or  less  chitinous  tendon 
(c.  t.)  which  arises  from  the  elastic  membrane.  Besides  these 
long  muscles  a  number  of  short  muscles  extend  between  the 
small  ventral  portion  of  the  pharynx  and  the  clypeus. 

The  food  of  thrips  is  of  a  liquid  nature  and  is  sucked  into  the 
oesophagus  in  the  following  manner,  judging  from  the  structure 
of  the  parts.  The  muscles  along  the  meson  of  the  elastic 
membrane  contract  and  dilate  the  lumen  of  the  pharynx  so 
that  a  partial  vacuum  is  formed,  and  into  this  cavity  is  sucked 
the  juice  in  which  the  tip  of  the  mouth-cone  is  immersed.  On 


50 


Annals  Entomological  Society  of  America    [Vol.  VIII, 


the  relaxation  of  the  dilating  muscles  the  elastic  membrane  forces 
the  food  dorsad  thru  the  open  valve  (v.)  into  the  oesophagus. 
A  more  detailed  account  will  be  given  of  this  process  in  the 
discussion  of  the  pharynx  of  Cephalothrips. 

Cephalothrips  yuccce. — In  a  similar  manner,  as  with  Helio- 
thrips,  figures  48-57  and  59  show  the  chief  characteristics  of 
the  pharynx  of  the  Tubulifera.  In  its  main  features  it  cor- 
responds with  the  general  description  of  the  pharynx  but  in  a 
few  details  it  shows  a  greater  degree  of  specialization  than  the 
pharynx  of  Heliothrips.  In  the  first  place  it  is  strikingly  ham- 
shaped  and  comparatively  smaller.  This  difference  in  size 
is  probably  due  to  the  reduction  of  the  mouth-cone.  Trans- 
verse sections  show  that  the  maxillary  guides  (mx.  g.)  unite 
with  the  pharynx  for  a  short  distance,  and  the  extension  over 
which  the  left  mandible  passes  is  the  cephalic  margin  of  the 
left,  maxillary  guide.  The  right,  rudimentary  mandible  (r.  md.) 
is  not  as  large  as  in  Heliothrips,  however,  it  still  retains  its  con- 
nection with  the  right  side  of  the  pharynx.  The  lumen  (1.) 
of  the  pharynx  is  straight.  The  most  striking  difference  between 
the  pharynx  of  Heliothrips  and  Cephalothrips  is  in  the  arrange- 
ment of  the  dilating  muscles. 

A  lateral  view  and  transverse  sections  of  the  pharynx 
show  a  distinct  chitinized  plate  (pt.)  standing  on  edge  along  the 
meson  of  the  elastic  membrane  (e.).  The  muscles  are  confined 
to  the  ventral  and  dorsal  ends  of  this  plate  and  the  majority 
of  them  are  connected  to  the  chitinous  tendon  (c.  t.)  at  the 
ventral  end.  These  muscles,  so-called  ventral  dilators  (v.  d.  m.), 
extend  into  the  head  and  unite  with  the  vertex.  There  is  a 
small  band  of  muscles,  the  so-called  dorsal  dilators  (d.  d.  m.), 
which  extend  between  the  dorsal  end  of  the  plate  and  the  caudo- 
ventral  area  of  the  front.  This  arrangement  of  muscles  is 
easily  derived  from  the  more  generalized  type  found  in  Helio- 
thrips. On  the  whole  the  form  and  arrangement  of  the  parts 
in  the  pharynx  of  Cephalothrips  would  suggest  that  it  is  a 
more  efficient  organ  than  that  of  Heliothrips. 

The  lumen  (1»)  of  the  alimentary  canal  is  cut  off  by  a  valve- 
like structure  at  the  dorsal  end  of  the  pharynx  (fig.  58a.).  A 
prominent ,  projection  (p.)  extends  from  the  caudo- dorsal  end 
of  the  pharynx  into  the  lumen.  This  projection  fits  into  a 
pocket  (po.)  on  the  opposite  side.    Under  normal  conditions 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  51 

this  valve  is  closed,  consequently  the  lumen  of  the  oesophagus 
is  cut  off  from  the  pharynx  while  the  elastic  membrane  is  dilated. 
In  suction  the  ventral  dilating  muscles  (v.  d.  m.)  contract  and 
pull  out  the  ventral  portion  of  the  elastic  membrane.  This 
results  in  the  formation  of  a  partial  vacuum,  and  into  this  space 
the  liquid  food  is  drawn.  The  dorsal  dilators  (d.  d.  m.)  now 
contract  and  dilate  the  dorsal  end  of  the  elastic  membrane 
(e.).  This  dilation  opens  the  valve  separating  the  lumen  of  the 
pharynx  and  the  oesophagus.  While  the  dorsal  dilators  are 
contracting  the  ventral  dilators  relax  and  the  ventral  portion 
of  the  elastic  membrane  presses  upon  the  enclosed  food.  This 
pressure  forces  the  food  dorsad  in  the  lumen  and  then  on  the 
relaxation  of  the  dorsal  dilators  the  elastic  membrane  falls 
back  into  its  normal  position  and  the  food  is  forced  on  and  into 
the  oesophagus.  This  completes  one  stroke  or  dilation  of  the 
pharynx  of  Cephalothrips. 

The  dilating  muscles  of  the  pharynx  (d.  m.)  of  Heliothrips,  as 
before  noted,  are  arranged  along  the  meson  of  the  elastic  mem- 
brane (e.).  This  fact,  along  with  the  large  size  of  the  pharynx 
and  its  peculiar  bent  condition,  would  indicate  that  the  elastic 
membrane  does  not  have  as  distinct  a  ventro-dorsal  dilation 
as  that  of  Cephalothrips.  Possibly  the  entire  central  portion 
of  the  membrane  is  dilated  at  one  time  and  then  as  the  large 
muscles  relax  the  few  strands  of  muscles  uniting  with  the 
pharynx  in  the  region  of  the  valve  contract  and  open  the  lumen. 
With  the  valve  open  and  the  elastic  membrane  pressing  upon 
the  enclosed  food,  the  plant  juice  is  forced  into  the  oesophagus. 

SALIVARY  GLANDS. 

Two  or  three  kinds  of  salivary  glands  (fig.  15,  16,  23,  24, 
30,  31,  38-44,  45,  49  and  51-55)  are  present  in  thrips  and 
these  are  all  located  in  the  thorax  and  abdomen.  Uzel  has 
figured  the  glandular  portion  of  the  salivary  glands  located 
in  the  thorax  and  abdomen  but  does  not  figure  the  course 
of  the  ducts.  In  Uzel's  figures  two  kinds  of  salivary  glands  are 
present  in  the  thorax  of  Aeolothrips  fasciatus,  a  form  belonging 
to  the  suborder  Terebrantia,  and  three  kinds  of  salivary  glands 
are  found  in  the  thorax  of  Trichothrips  copiosa,  a  form  belonging 
to  the  suborder  Tubulifera.  The  species  figured  in  this  paper 
have  only  two  kinds  of  salivary  glands,  which  extend  into  the 
thorax  and  abdomen.    These  two  kinds  are  paired  and  distinct. 


52  Annals  Entomological  Society  of  America    [Vol.  VIII, 

Considerable  variation  occurs  in  regard  to  the  exact  location  of 
these  glands  and  the  position  and  points  of  union  of  their  ducts. 

One  of  the  two  pairs  of  salivary  glands  (fig.  15  and  24,  31) 
in  the  thorax  and  .abdomen  of  the  two  species  here  considered 
is  long,  tubular  and  more  or  less  homogenous  thruout  its  length 
1.  s.  g.).  This  pair  is  located  laterad  or  dorsad  of  the  alimentary 
canal  and  continues  caudad  into  the  abdomen.  Longitudinal 
sections  thru  these  glands  show  that  they  are  homogenous, 
nucleated  and  apparently  syncitial. 

The  second  pair  of  salivary  glands  (fig.  16  and  30)  are  short, 
thick  and  more  or  less  irregular  in  outline  and  usually  confined 
to  the  thorax  (s.  s.  g.).  The  cells  of  these  glands  are  large  and 
the  cell  walls  are  distinct.  The  nuclei  are  prominent  and 
stain  deeply.  The  protoplasm  of  the  tissue  stains  un- 
evenly and  is  more  or  less  filled  with  vacuoles.  A  distinct 
centrally  located  lumen  extends  thruout  the  entire  length  of  the 
gland. 

The  above  two  pairs  of  salivary  glands  give  rise  to  ducts 
(1.  d.  and  s.  d.)  at  their  cephalic  ends.  The  four  ducts  extend 
into  the  head  laterad  and  dorsad  of  the  oesophagus.  In  the 
region  between  the  supraoesophageal  and  suboesophageal 
ganglia  the  ducts  turn  ventrad  and  continue  to  the  y-shaped 
chitinous  structure  (y.)  caudad  of  the  pharynx  (fig.  23,  45,  49, 
58  and  59.).  Within  this  structure  or  before  entering  it  the 
four  ducts  unite  into  a  common  duct  and  this  common  duct 
(c.  d.)  continues  ventrad  to  the  apex  of  the  mouth-cone.  The 
secretions  from  the  salivary  glands  are  thus*  poured  into  the 
punctures  in  the  host  plant  which  are  made  by  the  mouth-parts. 
When  thrips  puncture  green  leaves  or  colored  flowers  the  area 
about  the  puncture  becomes  light  in  color.  This  discoloration 
is  undoubtedly  due  to  the  action  of  the  salivary  secretion  on 
the  plant  tissue. 

The  y-shaped  piece  (y.)  caudad  of  the  pharynx  in  all  thrips 
is  a  characteristic  structure.  In  both  suborders  this  piece  is 
somewhat  different  in  shape  (fig.  35  and  47)  but  it  has  the  same 
relation  to  the  mouth-parts.  There  is  a  distinct  muscle  band 
or  there  may  be  several  bands  (mu.)  extending  between  the 
base  of  the  arms  of  the  y  and  the  dorsal  part  of  the  caudal  aspect 
of  the  pharynx  (ph.).  Possibly,  on  contraction,  these  muscles 
move  the  y-shaped  piece  in  such  a  manner  as  to  control  the  flow 
from  the  salivary  glands.    The  exact  homology  of  the  y-shaped 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  53 

structure  is  not  clear  but  its  general  position  and  structure, 
its  opening  into  the  mouth-cavity  and  its  relation  to  the  sali- 
vary ducts  would  indicate  that  it  is  homologous  with  the  salivary 
syringe  of  the  Hemiptera. 

Heliothrips  femoralis. — The  long,  narrow,  tube-like  glands 
(fig.  31  and  24)  are  located  laterad  of  the  alimentary  canal 
(1.  s.  g.)  and  extend  from  the  metathorax  caudad  to  about  the 
fourth  abdominal  segment.  Figure  24  shows  that  the  gland  is 
narrow  and  has  a  straight  lumen  extending  thruout  its  length. 
The  ducts  from  these  glands  (fig.  31,  1.  d.)  are  enlarged  and 
located  dorsad  of  the  oesophagus  in  the  region  of  the  pro- 
thorax  and  mesothorax.  The  enlarged  portions  of  the  ducts 
serve  as  reservoirs  for  the  secretion.  The  ducts  from  these 
similar  right  and  left  glands  unite  with  each  other  before 
entering  the  y-shaped  structure  caudad  of  the  pharynx. 

The  short,  thick,  oval  glands  (fig.  30,  s.  s.  g.)  in  the  thorax 
are  about  the  length  of  two  segments  and  located  laterad  of  the 
oesophagus.  The  right  gland  is  usually  confined  to  the  meta- 
thorax and  the  first  abdominal  segment.  The  cells  of  these 
glands  are  exceedingly  large  and  distinctly  differentiated. 
One  or  two  deeply  staining,  irregular  nuclei  can  be  seen  in  each 
cell,  and  the  protoplasm  of  the  cells  stains  more  or  less  unevenly. 
The  ducts  from  these  glands  (s.  d.)  have  about  the  same  thick- 
ness thruout.  In  the  region  of  the  head  they  are  somewhat 
larger  than  the  ducts  from  the  above  glands  in  the  same  region. 
The  duct  from  the  left  gland  unites  with  the  duct  from  the 
right  similar  gland  before  entering  the  y-shaped  piece  (fig.  40, 
45  and  58).  Within  the  y-shaped  piece  the  united  ducts  from 
the  two  kinds  of  glands  join  and  form  a  common  duct  which 
continues  to  nearly  the  apex  of  the  mouth-cone. 

Cephalothrips  yucca. — The  long,  tube-like  glands  of  Cephalo- 
thrips  (fig.  15,  1.  s.  g.)  are  located  laterad  of  the  alimentary 
canal  and  extend  from  the  prothorax  into  the  first  or  second 
abdominal  segment.  These  glands  are  homologous  with  the 
long,  tube-like  glands  in  Heliothrips,  but  they  are  thicker 
and :  have  a  sinuous  lumen  thruout  their  length.  The  cell 
consistency  is  about  the  same  as  in  Heliothrips.  The  ducts 
extending  from  these  glands  into  the  head  are  very  small  and 
not  dilated  in  the  thorax. 


54  Annals  Entomological  Society  of  America    [Vol.  VIII, 


The  short,  thick  glands  (fig.  16,  s.  s.  g.)  in  the  thorax  of 
Cephalothrips  are  usually  confined  to  the  mesothorax  and 
metathorax  and  located  laterad  of  the  alimentary  canal.  These 
glands  are  homologous  with  the  short,  thick  glands  of  Helio- 
thrips.  In  Cephalothrips  these  glands  are  longer  and  made 
up  of  smaller  cells  filled  with  vacuoles  and  granulated  areas. 
The  ducts  from  these  glands  (fig.  23)  are  of  the  same  consistency 
thruout  and  only  slightly  larger  than  the  ducts  from  the  long 
tubular  glands.  The  union  of  the  salivary  ducts  in  the  head 
is  somewhat  different  from  that  of  Heliothrips.  The  ducts 
(fig.  23,  49,  52-55  and  59)  of  one  side  (1.  d.  and  s.  d.)  unite  and 
these  united  ducts  meet  in  the  center  of  the  mouth-cone  and 
form  a  common  duct  (c.  d.)  before  entering  the  y-shaped  piece. 

HEAD- GLANDS. 

A  distinct,  multinucleated  and  deeply  staining  tissue  (h.  g.) 
is  present  in  definite  parts  of  the  head  and  mouth-cone  of 
thrips  and  so  far  as  known  is  described  here  for  the  first  time 
(fig.  26,  38-43,  45,  49,  51-55,  58  and  59).  This  tissue,  as 
far  as  can  be  determined,  is  of  a  glandular  nature  and  it  will 
be  here  designated  as  the  head-gland.  Its  histological  struc- 
ture is  different  from  that  of  the  thoracic  glands.  Num- 
erous and  coarsely  granulated  nuclei  are  present;  the  cell  walls 
cannot  be  differentiated;  the  protoplasm  stains  unevenly  and 
no  lumen  could  be  identified.  This  tissue  is  most  abundant 
in  the  members  of  the  suborder  Terebrantia.  In  Heliothrips 
(fig.  26,  38-43,  45  and  58)  it  occurs  in  three  distinct  regions. 
The  most  prominent  massing  occurs  cephalad  of  the  pharynx 
(h.  g.)  on  the  two  sides  of  the  dilating  muscles.  The  extent 
and  shape  of  these  two  masses  varies  considerably  but  the 
figures  of  the  transverse  sections  and  the  lateral  views  of  the 
pharynx  show  the  usual  distribution  in  this  area.  Distinct 
ducts  (d.)  arise  from  the  dorsal  ends  of  these  masses  and  ex- 
tend around  the  lateral  sides  of  the  oesophagus  and  turn  ven- 
trad  and  enter  the  two  small  openings  on  the  caudal  aspect 
of  the  pharynx  (fig.  27,  45,  46  and  58).  If  the  above  masses  are 
glandular  then  one  can  readily  see  how  their  secretions  may  be 
poured  into  the  pharynx  and  aid  in  digestion.  Besides  the 
above  glandular  masses  cephalad  of  the  pharynx,  similar  tissue 
is  present  at  the  proximal  end  of  the  left  and  right  mandibles. 


1915] 


The  Head  and  Mouth-Parts  of  Thysanoptera 


55 


The  small  mass  on  the  left  side  (fig.  26)  projects  for  a  short 
distance  into  the  hollow  cavity  of  the  left  mandible.  This 
is  not  the  case  with  the  mass  adjacent  to  the  right,  rudimentary 
mandible.  These  two  small  masses  are  connected  with  the 
masses  above  described  by  means  of  fine  ducts  (du.).  The 
exact  extent  of  these  ducts  has  not  been  definitely  determined. 
It  is  possible  that  they  unite  with  the  ducts  entering  the  pharynx. 
It  is  also  possible  that  the  secretions  from  the  small  mass  within 
the  left  mandible  passes  out  thru  the  minute  lumen  of  the 
mandible.  In  the  concave  portion  of  the  labrum  small  masses 
of  tissue  are  present  which  resemble  the  above  so-called  gland- 
ular tissue.  The  extent  of  these  masses  varies  and  as  yet  no 
ducts  have  been  observed  in  connection  with  them. 

In  Cephalothrips  (fig.  48,  49-51,  55  and  59)  the  above  sup- 
posed glandular  tissue  of  the  head  is  present  but  it  is  not  so  exten- 
sive. Two  distinct  masses  can  be  identified  cephalad  of  the 
pharynx  and  these  give  rise  to  ducts  (d.)  that  empty  into  the 
pharynx  as  in  Heliothrips.  Also  a  small  mass  of  similar  tissue 
is  located  at  the  base  of  the  left  mandible  but  no  such  mass 
is  found  on  the  right  side  near  the  right  mandible.  No  glandu- 
lar tissue  was  found  in  the  concave  portion  of  the  labium  as 
in  Heliothrips. 

SUMMARY. 

1.  The  general  arrangement  of  the  head  and  mouth-parts 
of  the  Thysanoptera  and  the  Hemiptera  is  similar. 

2.  The  resemblance  between  the  mouth-parts  of  Thysan- 
optera and  Orthoptera  is  apparently  closer  than  the  resemblance 
between  the  mouth-parts  of  Hemiptera  and  Orthoptera. 

3.  A  comparison  of  the  different  structures  of  the  two 
suborders  shows  clearly  that  the  suborder  Terebrantia  is  more 
generalized  than  the  suborder  Tubulifera. 

4.  The  mouth-parts  of  thrips  are  fitted  for  sucking. 

5.  The  parts  of  the  mouth  are  in  the  form  of  a  cone  which 
encloses  the  piercing  organs.  The  cone  is  composed  of  the 
clypeus  (cl.)  labrum  (lr.),  maxillary  sclerites  (mx.  s.)  and  labium 

db.). 

6.  The  mouth-parts  of  thrips  are  asymmetrical. 

7.  The  asymmetry  of  the  clypeus  (cl.)  and  the  maxillary 
sclerites  (mx.  s.)  in  the  two  suborders  is  of  an  entirely  different 
nature. 


56  Annals  Entomological  Society  of  America    [Vol.  VIII , 

8.  The  left  asymmetrical  piercing  organ  (1.  md.)  is  the  left 
mandible  and  the  right,  rudimentary  piece  (r.  md.)  extending 
between  the  pharynx  (ph.)  and  the  front  (fr.)  is  the  right, 
rudimentary  mandible.  These  mandibular  parts  are  present 
in  all  thrips  as  far  as  observed. 

9.  A  pair  of  maxillae  are  present  in  all  thrips.  Each 
maxilla  is  divided  into  two  parts;  the  asymmetrical  or  sym- 
metrical, palpus-bearing,  maxillary  sclerite  (mx.  s.)  and  the 
symmetrical  maxillary  seta  (mx.). 

10.  The  tentorial  structures  in  the  nymph  of  Heliothrips 
can  be  homologized  with  the  tentorium  of  Cicada.  On  the 
basis  of  this  homology  ,  the  greatly  reduced  tentorium  of  adult 
thrips  can  be  interpreted. 

11.  The  usual  association  between  the  tentorium  and  the 
mouth-parts  in  generalized  insects  is  present  in  thrips  and  aids 
in  interpreting  the  piercing  organs.  The  maxillary  setae  are 
closely  associated  with  the  posterior  arms,  while  the  left  and 
right  mandibles  are  associated  with  the  invaginations  of  the 
anterior  arms  of  the  tentorium. 

12.  A  comparison  of  the  head  of  the  nymph  of  Cephalo- 
thrips  and  the  head  of  the  adult  of  Heliothrips  shows  clearly  the 
homology  existing  between  the  two  suborders  in  respect  to  the 
piercing  organs. 

13.  The  semi-pupal  stage  of  Cephalothrips  shows  a  distinct 
reduction  in  the  mouth-corie.  The  peculiar  shape  of  the  left 
mandible  and  the  point  of  attachment  of  the  maxillary  setae 
in  the  adult  is  in  part  due  to  this  reduction. 

14.  The  pharynx  at  the  anterior  end  of  the  alimentary 
canal  is  modified  into  a  distinct  and  characteristic  sucking 
apparatus. 

15.  Two  kinds  of  paired  salivary  glands  are  found  in  the 
thorax  and  abdomen  of  the  two  species  here  figured.  The 
ducts  from  these  glands  unite  and  pass  into  a  y-shaped  structure 
caudad  of  the  pharynx. 

16.  The  tissue  in  the  head,  here  called  head-glands,  has  a 
similar  structure  and  a  definite  arrangement.  Ducts  can  be 
traced  from  the  majority  of  these  glands  to  the  two  small  open- 
ings on  the  caudal  aspect  of  the  pharynx. 


1915] 


The  Head  and  Mouth-Parts  of  Thysanoptera 


57 


BIBLIOGRAPHY. 

Berlese,  Antonio. — Gli  Insetti,  loro  organizzazione,  sviluppo,  abitudini  e  rapporti 

coll'uomo.    Vol.  I.,  Milan,  1909,  153. 
Bugnion,  E. — L'Appareil  Salivaire  des  Hemipteres.    Arch.  D'Anat.  Mic.  Vol.  10, 

1908,  227-268;  Vol.  11,  1910,  435-456. 
Faure-Fremiet,  E. — Contribution  a  L'Etude  des  Glandes  Labiales  des  Hydrocor- 

ises.    Ann.  des  Sci.  Nat.  Zool.,  N.  S.  9,  Vol.  12,  1910,  217-239. 
Garman,  H. — The  Mouth-parts  of  the  Thysanoptera.    Bui.  of  the  Essex  Inst. 

Vol.  22,  1890,  24-27. 

Hinds,  W.  E. — Contribution  to  a  Monograph  of  the  Insects  of  the  Order  Thy- 
sanoptera Inhabiting  North  America.  Proc.  of  the  U.  S.  Nat.  Mus.  Vol.  26, 
1903,  79-242. 

Jordan,  Karl. — Anatomie  und  Biologie  der  Physapoda.  Zeit.  fur  Wiss.  Zool.  Vol. 
47,  1888,  541-620. 

Muir,  F.  and  Kershaw,  J.  C. — On  the  Homologies  and  Mechanism  of  the  Mouth- 
parts  of  Hemiptera.  Psyche.    Vol.  18,  1911,  9-10. 
Uzel,  Heinrich. — Monographic  der  Ordnung  Thysanoptera.  1895. 


EXPLANATION  OF  PLATES. 


Plate  I. 


Fig.  1.  Ventral  aspect  of  the  head  of  Heliothrips  femoralis. 

Fig.  2.  Left  later  1  aspect  of  the  head  of  leliothrips  femoralis. 

Fi  [.  3.  Left  lateral  aspect  of  the  mouth-cone  of  Thrips  physapus. 

Fig.  4.  Antenna  of  Heliothrips  femoralis. 

Fig.  5.  Right  lateral  aspect  of  the  head  of  Heliothrips  femoralis. 

Fig.  6.  Right  lateral  aspect  of  the  mouth-cone  of  Thrips  physapus. 

Fig.  7.  Dorsal  aspect  of  the  head-capsule  of  Heliothrips  femoralis. 


Plate  II. 

Fig.   8.    Ventral  aspect  of  the  head  of  Cephalothrips  yuccas. 

Fig.   9.    Dorsal  aspect  of  the  head-capsule  of  Cephalothrips  yuccas. 

Fig.  10.    Antenna  of  Cephalothrips  yuccae. 

Fig.  11.    Left  lateral  aspect  of  the  head  of  Cephalothrips  yuccae. 


Plate  III. 

Fig.  12.    Left  lateral  aspect  of  the  head  of  the  nymph  of  Heliothrips  femoralis. 
Fig.  13.    Ventral  aspect  of  the  head  of  the  nymph  of  Heliothrips  femoralis. 
Fig.  14.    Ental  view  of  a  maxillary  sclerite  of  Thrips  physapus. 
Fig.  15.    Longitudinal  section  of  the  proximal  and  distal  portions  of  a  long, 

salivary  gland  of  Cephalothrips  yuccas. 
Fig.  16.    Longitudinal  section  of  a  short,  salivary  gland  of  Cephalothrips  yuccae. 
Fig.  17.    Ventral  aspect  of  the  head  of  the  nymph  of  Cephalothrips  yuccae. 
Fig.  18.    Left  lateral  aspect  of  the  head  of  the  nymph  of  Cephalothrips  yuccae. 
Fig.  19.    Right  lateral  aspect  of  the  head  of  the  nymph  of  Heliothrips  femoralis. 
Fig.  20.    Ventral  aspect  of  the  head  of  the  semi-pupa  of  Cephalothrips  yuccae. 
Fig.  21.    Ectal  aspect  of  a  maxillary  sclerite  of  Frankliniella  tritici. 


58 


Annals  Entomological  Society  of  America    [Vol.  VIII, 


Plate  IV. 

Fig.  22.    Ental  view  of  the  ventral  aspect  of  the  mouth-cone  and  a  portion  of 

the  head-capsule  of  the  nymph  of  Cephalothrips  yuccae.    The  parts 

have  been  spread  and  the  pharynx  omitted. 
Fig.  23.    The  union  of  the  salivary  ducts  in  Cephalothrips  yuccae.    The  solid 

lines  indicate  the  structures  in  a  sagittal  section,  ten  microns  thick. 
Fig.  24.    Distal  portion  of  a  longitudinal  section  of  the  long  salivary  glands  of 

Heliothrips  femoralis. 
Fig.  25.    Manner  of  interlocking  of  the  grooved  maxillary  setae  of  Cephalothrips 

yuccae  when  projected  from  the  mouth-cone. 
Fig.  26.    Sagittal  section  of  the  left,  asymmetrical  mandible  of  Heliothrips 

femoralis. 

Fig.  27.    Ental  view  of  the  ventral  aspect  of  the  mouth-cone  and  a  portion  of  the 

head-capsule  of  Heliothrips  femoralis.    The  parts  have  been  spread 

and  the  maxillary  extensions  (et.)  omitted. 
Fig.  28.    Ental  view  of  the  ventral  aspect  of  the  mouth-cone  and  a  portion  of  the 

head-capsule  of  the  nymph  of  Heliothrips  femoralis.    The  parts  have 

been  spread  and  the  pharynx  omitted. 
Fig.  29.    The  tentorium  of  Cicada  septendecim. 

Fig.  30.  Longitudinal  section  of  the  short  salivary  gland  of  Heliothrips  femoralis. 
Fig.  31.    Longitudinal  section  thru  a  dilated  duct  of  a  long  salivary  gland  of 

Heliothrips  femoralis.    The  distal  portion  of  the  gland  shown  in 

figure  24. 

Fig.  32.    Ental  view  of  the  right  maxillary  sclerite  of  Heliothrips  femoralis. 


Plate  V. 

Fig.  33.  Ental  view  of  the  ventral  aspect  of  the  mouth-cone  and  a  portion  of  the 
head-capsule  of  Cephalothrips  yuccae.  The  parts  have  been  spread 
and  the  pharynx  omitted. 

Fig.  24.    Ental  aspect  of  the  left  maxillary  sclerite  of  Cephalothrips  yuccae. 

Fig.  35.  Ental  view  of  the  ventral  aspect  of  the  mouth-cone  of  Cephalothrips 
yuccae.    The  parts  have  been  spread. 

Fig.  36.    Ental  aspect  of  the  right  maxillary  sclerite  of  Cephalothrips  yuccae. 

Plate  VI. 

Fig.  37.  Frontal  section  thru  the  commissures  connecting  the  supraoesophageal 
and  suboesophageal  ganglia  of  Heliothrips  femoralis. 

Fig.  38-44.  Cross-sections  of  the  pharynx  from  the  dorsal  end  to  the  tip  of  the 
mouth-cone  of  Heliothrips  femoralis.  Each  second  or  third  section 
figured. 

Fig.  45.    Lateral  view  of  the  pharynx  of  Heliothrips  femoralis. 

Fig.  46.    Caudal  aspect  of  the  pharynx  of  Heliothrips  femoralis.    The  extensions 

over  which  the  maxillary  setae  pass,  have  been  omitted. 
Fig  47.    Caudal  aspect  of  the  Y-shaped  piece  located  caudad  of  the  pharynx. 
Fig.  48.    Caudal  aspect  of  the  pharynx  and  labrum  of  Cephalothrips  yuccae. 

The  extensions,  over  which  the  maxillary  setae  and  left  mandible 

pass,  have  been  omitted. 
Fig.  49.    Lateral  view  of  the  pharynx  of  Cephalothrips  yuccae. 
Fig.  50.    Frontal  section  thru  the  commissures  connecting  the  supraoesophageal 

and  suboesophageal  ganglia  of  Cephalothrips  yuccae. 
Fig.  51.    Cross-section  of  the  oesophagus  of  Cephalothrips  yuccae  at  the  point 

where  ducts  from  the  head-glands  (d.)  pass  laterad  of  the  oesophagus 

in  their  extension  from  the  head-glands  to  the  two  openings  on  the 

caudal  aspect  of  the  pharynx. 
Fig.  52-57.    Cross-sections  of  the  pharynx  from  the  dorsal  end  to  the  tip  of  the 

mouth-cone  of  Cephalothrips  yuccae.    Each  second  or  third  section 

figured. 


1915]        The  Head  and  Mouth-Parts  of  Thysanoptera  59 


Plate  VII. 

Fig.  58.    Sagittal  section  thru  the  head  and  prothorax  of  Heliothrips  femoralis. 

The  salivary  glands  have  been  omitted. 
Fig.  58a.  The  valve  at  the  dorsal  end  of  the  pharynx  of  figure  58  more  enlarged. 
Fig.  59.    Sagittal  section  thru  the  head  and  a  portion  of  the  prothorax  of  Cephalo- 

thrips  yuccae.    The  salivary  glands  have  been  omitted. 
Fig.  60.    Caudal  aspect  of  the  labium  of  Heliothrips  femoralis. 
Fig.  61.    Caudal  aspect  of  the  labium  of  Cephalothrips  yuccae. 


LIST  OF  ABBREVIATIONS. 


a.  a. 

Anterior  arms  of  the  tentorium. 

mx.  g. 

Maxillary  guide. 

al.  c. 

Alimentary  canal. 

mx.  p. 

Maxillary  pillar. 

ant. 

Antennae. 

mx.  pi. 

Maxillary  palpus. 

c.  a. 

Caudal  projections  or  arms. 

mx.  s. 

Maxillary  scierite. 

c.  d. 

Common  duct  of  the  salivary 

n. 

Notch. 

glands. 

ne. 

Nerve. 

cl. 

Clypeus. 

o. 

Occiput. 

CO. 

Commissure. 

oc. 

Ocellus. 

c.  t. 

Chitinous  tendon. 

oe. 

Oesophagus. 

d. 

Duct  of  the  head-glands. 

on. 

Oenocyte. 

d.  a. 

Dorsal  arms  of  the  tentorium. 

p. 

Pharyngeal  projection. 

d.  d.  m. 

Dorsal  dilating  muscles  of  the 

p.  a. 

Posterior  arms  of  the  tentorium. 

pharynx. 

ph. 

Pharynx. 

d.  1. 

Dilated  lumen. 

P.  1. 

Prothoracic  leg. 

d.  m. 

Dilating  muscles  of  the  pharynx. 

po. 

Pharyngeal  pocket. 

du. 

Duct  from  glandular  tissue  near 

pr. 

Paraglossa. 

mandible. 

p.  s. 

Prothoracic  scierite. 

e. 

Elastic  membrane. 

pt. 

Chitinous  plate. 

et. 

Ental  extensions  of  the  maxil- 

r. md. 

Right  rudimentary  mandible. 

lary  sclerites. 

rt. 

Reticulation. 

f. 

Fold  in  the  clypeus. 

s. 

Suture. 

fr. 

Front. 

s.  c. 

Sense  cone. 

g- 

Gena. 

s.  d. 

Duct  of  the  short  salivary  gland 

h.  g. 

Head-glands. 

sm. 

Submentum. 

i.  a. 

Invaginations  of  the  anterior 

s.  s.  g. 

Short  salivary  gland. 

arms  of  the  tentorium. 

St. 

Caudal  head-strip. 

i.  d. 

Invaginations    of    the  dorsal 

sub. 

Suboesophageal  ganglion. 

arms  of  the  tentorium. 

supra. 

Supraoesophageal  ganglion. 

i.  p. 

Invaginations  of  the  posterior 

t. 

Thorax. 

arms  of  the  tentorium. 

t.  a. 

Transverse  area  of  the  pharynx. 

1. 

Lumen. 

v.  d.  m. 

Ventral,    dilating  muscles  of 

lb. 

Labium. 

pharynx. 

lb.  pi. 

Labial  palpus. 

vt. 

Vertex. 

L  d. 

Duct  of  the  long,  salivary  gland. 

X. 

Ental  thickening  on  margin  of 

1.  et. 

Ental  extensions  of  the  labium. 

head-capsule. 

1.  md. 

Left  mandible. 

xc. 

Union  of  the  anterior  and  pos- 

lr. 

Labium. 

terior  arms. 

L  s.  g. 

Long  salivary  gland. 

y. 

Y-shaped  pharyngeal  piece. 

m. 

Men  turn. 

z. 

Ental  thickening  on  margin  of 

me. 

Membranous  area. 

head-capsule. 

mu. 

Muscle. 

zc. 

Piece  connecting    the  united 

mx. 

Maxillary  seta. 

arms. 

Annals  E.  S.  A. 


Vol.  VIII,  Plate  I. 


Alvah  Peterson. 


Annals  E.  S.  A. 


Vol.  VIII,  Plate  II. 


Alvah  Peterson. 


Annals  E).  S.  A. 


Vol.  VIII,  Plate  III. 


Alvah  Peterson. 


Annals  E.  S.  A. 


Vol.  VIII,  Plate  IV. 


Alvah  Peterson, 


Annals  E.  S.  A. 


Vol.  VIII,  Plate  V. 


Alvah  Peterson. 


Annals  E.  S.  A. 


Vol.  VIII.  Plate  VI. 


Alvah  Peterson. 


Annals  E-  vS.  A. 


Vol.  VIII,  Plate  VII. 


Alvah  Peterson. 


? 


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